A Comparison of hp-adaptive 

Strategies for Elliptic Partial 

Differential Equations (Long Version) 

William F. Mitchell 

Marjorie A. McClain 

NISTIR 7824 
NISTIR 7824 

A Comparison of hp-adaptive 

Strategies for Elliptic Partial 

Differential Equations (Long Version) 

 

William F. Mitchell 

Marjorie A. McClain

Information Technology Laboratory 

Applied and Computational Sciences Division 

 

October 2011 

U.S. Department of Commerce 

Rebecca M. Blank, Acting Secretary 

National Institute of Standards and Technology 

Patrick D. Gallagher, Under Secretary for Standards and Technology and Director 
A Comparison of hp-Adaptive Strategies for Elliptic Partial

Differential Equations (Long Version)

William F. Mitchell∗

Marjorie A. McClain

Applied and Computational Mathematics Division

National Institute of Standards and Technology

Gaithersburg, MD 20899-8910

Abstract

The hp version of the finite element method (hp-FEM) combined with adaptive mesh refinement is a

particularly efficient method for solving partial differential equations because it can achieve a convergence

rate that is exponential in the number of degrees of freedom. hp-FEM allows for refinement in both the

element size, h, and the polynomial degree, p. Like adaptive refinement for the h version of the finite

element method, a posteriori error estimates can be used to determine where the mesh needs to be refined,

but a single error estimate can not simultaneously determine whether it is better to do the refinement by h

or by p. Several strategies for making this determination have been proposed over the years. In this paper

we summarize these strategies and present the results of a numerical experiment to study the convergence

properties of these strategies.

Keywords: elliptic partial differential equations, finite elements, hp-adaptive strategy, hp-FEM

1 Introduction

The numerical solution of partial differential equations (PDEs) is the most compute-intensive part of a wide

range of scientific and engineering applications. Consequently the development and application of faster and

more accurate methods for solving partial differential equations has received much attention in the past fifty

years. Many of the applications at the cutting edge of research are extraordinarily challenging. For these

problems it is necessary to allocate computing resources in an optimal way in order to have any chance at

solving the problem. Determining the best grid and approximation space on which to compute the solution

is a central concern in this regard. Unfortunately, it is rarely possible to determine an optimal grid in

advance. Thus, developing self-adaptive techniques which lead to optimal resource allocation is critical for

future progress in many fields.

Self-adaptive methods have been studied for over 30 years now. They are often cast in the context of

finite element methods, where the domain of the PDE is partitioned into a mesh consisting of a number of

elements (in two dimensions, usually triangles or rectangles), and the approximate solution is a polynomial

over each element. Most of the work has focused on h-adaptive methods. In these methods, the mesh size,

∗Contribution of NIST, not subject to copyright.

1
h, is adapted locally by means of a local error estimator with the goal of placing the smallest elements in the

areas where they will do the most good. In particular, elements that have a large error estimate get refined

so that ultimately the error estimates, and presumably the error, are approximately equal over all elements.

h-adaptive methods are quite well understood now, and are beginning to be used in practice.

Recently, the research community has begun to focus more attention on hp-adaptive methods. In these

methods, one not only locally adapts the size of the mesh, but also the degree of the polynomials, p. The

attraction of hp-adaptivity is that the error converges at an exponential rate in the number of degrees of

freedom, as opposed to a polynomial rate for fixed p. Much of the theoretical work showing the advantages

of hp-adaptive methods was done in the 1980’s, but it wasn’t until the 1990’s that practical implementation

began to be studied. The new complication is that the local error estimator is no longer sufficient to guide

the adaptivity. It tells you which elements should be refined, but it does not indicate whether it is better to

refine the element by h or by p. A method for making that determination is called an hp-adaptive strategy.

A number of strategies have been proposed, but it is not clear which ones perform best under different

situations, or even if any of the strategies are good enough to be used as a general purpose solver. In this

paper we present an experimental comparison of several hp-adaptive strategies.

Any study of this type is necessarily limited in scope. The comparison will be restricted to steady-state

linear elliptic partial differential equations on bounded domains in two dimensions with Dirichlet, natural

or mixed boundary conditions. The standard Galerkin finite element method will be used with the space

of continuous piecewise polynomial functions over triangles that are refined by the newest node bisection

method.

The remainder of the paper is organized as follows. In Section 2 we define the equation to be solved, present

the finite element method, and give some a priori error estimates. In Section 3 we give the details of the

hp-adaptive finite element algorithm used in the experiments. Section 4 defines the hp-adaptive strategies to

be compared. Section 5 contains the results of the experiments. Finally, we draw our conclusions in Section

6.

2 The Finite Element Method

We consider the elliptic partial differential equation

Lu = −

∂

∂x 

p(x, y)

∂u

∂x

−

∂

∂y 

q(x, y)

∂u

∂y 

+ r(x, y)u = f(x, y) in Ω (1)

u = gD(x, y) on ∂ΩD (2)

Bu = p(x, y)

∂u

∂x

∂y

∂s − q(x, y)

∂u

∂y

∂x

∂s + c(x, y)u = gN (x, y) on ∂ΩN (3)

where Ω is a bounded, connected, polygonal, open region in R

2 with boundary ∂Ω = ∂ΩD ∪ ∂ΩN , ∂ΩD ∩

∂ΩN = ∅. Differentiation with respect to s is with respect to a counterclockwise parameterization of the

boundary (x(s), y(s)) with k(dx/ds dy/ds)k = 1. If c = 0 Equation 3 is the natural boundary condition.

If, in addition, p = q = 1 or ∂ΩN consists of line segments that are parallel to the axes, Equation 3 is

the Neumann boundary condition. We assume the data in Equations 1-3 satisfy the usual ellipticity and

regularity assumptions. In one of the test problems, we extend the equation to a system of two equations

containing a cross derivative term ∂

2u/∂x∂y, and in another test problem we include first order derivative

terms.

2
As usual, define the space L

2 by

L

2

(Ω) = {v(x, y) : ZZ

Ω

v

2

dx dy < ∞}

with inner product

hu, vi2 =

ZZ

Ω

uv dx dy

and norm

||v||2

2 = hv, vi2.

We denote by Hm(Ω) the usual Sobolov spaces

Hm(Ω) = {v ∈ L

2

(Ω) : Dαv ∈ L

2

(Ω), |α| ≤ m}

where

Dαv =

∂

|α|v

∂

α1 x∂α2 y

, α = (α1, α2), αi ∈ N, |α| = α1 + α2.

The Sobolov spaces have inner products

hu, viHm(Ω) =

ZZ

Ω

X

|α|≤m

DαuDαv dx dy

and norms

||v||2

Hm(Ω) = hv, viHm(Ω).

We will also refer to the seminorm |v|Hm(Ω) where the sum is over |α| = m.

Let Hm

0

(Ω) = {v ∈ Hm(Ω) : v = 0 on ∂ΩD}. Let  ̃uD be a lift function satisfying the Dirichlet boundary

conditions in Equation 2 and define the affine space  ̃uD +H1

0

(Ω) = {u ̃D +v : v ∈ H1

0

(Ω)}. Define the bilinear

form

B(u, v) = ZZ

Ω

p

∂u

∂x

∂v

∂x + q

∂u

∂y

∂v

∂y + ruv dx dy +

Z

∂ΩN

cuv ds

and the linear form

L(v) = ZZ

Ω

fv dx dy +

Z

∂ΩN

gN v ds

Then the variational form of the problem is to find the unique u ∈ u ̃D + H1

0

(Ω) that satisfies

B(u, v) = L(v) ∀v ∈ H1

0

(Ω).

The energy norm of v ∈ H1

0

is defined by ||v||2

E(Ω) = B(v, v).

The finite element space is defined by partitioning Ω into a grid (or mesh), Ghp, consisting of a set of NT

triangular elements, {Ti}

NT

i=1 with Ω =  ̄ ∪

NT

i=1T ̄

i

. If a vertex of a triangle is contained in the interior of an

edge of another triangle, it is called a hanging node. We only consider compatible grids with no hanging

nodes, i.e. T ̄

i ∩T ̄j , i 6= j, is either empty, a common edge, or a common vertex. The diameter of the element

is denoted hi. With each element we associate an integer degree pi ≥ 1. The finite element space Vhp is

3
the space of continuous piecewise polynomial functions on Ω such that over element Ti

it is a polynomial

of degree pi. The degree of an edge is determined by applying either a minimum rule or a maximum rule

over Ghp in which the edge is assigned the minimum or maximum of the degrees of the adjacent elements,

respectively.

The finite element solution is the unique function uhp ∈ u ̃D + Vhp that satisfies

B(uhp, vhp) = L(vhp) ∀vhp ∈ Vhp.

The error is defined by ehp = u − uhp.

The finite element solution is expressed as a linear combination of basis functions {φi}

N

i=1 that span

u ̃D + Vhp,

uhp =

X

N

i=1

αiφi(x, y)

For high order elements, there are a number of basis sets used in practice. A number of the hp strategies of

Section 4 rely on the basis being a p-hierarchical basis in which the basis functions for a space of degree p

are a subset of the basis functions for a space of degree p + 1. In the results of Section 5 the p-hierarchical

basis of Szabo and Babuˇska [33], which is based on Legendre polynomials, is used. Regardless of the choice

of basis set, for an element of degree pi with edge degrees pi,j , j = 1, 2, 3, there is one linear basis function

associated with each vertex, pi,j − 1 basis functions (one each of degree 2, 3 . . . pi,j ) associated with edge j,

and q − 2 basis functions of degree q for q = 3, 4 . . . pi (for a total of (pi − 1)(pi − 2)/2) whose support is the

interior of the triangle.

The discrete form of the problem is a linear system of algebraic equations

Ax = b (4)

where the matrix A is given by Aij = B(φi, φj ) and the right hand side is given by bi = L(φi).

If h and p are uniform over the grid, u ∈ Hm(Ω), and the other usual assumptions are met, then the a

priori error bound is [6, 7]

||ehp||H1(Ω) ≤ C

h

μ

pm−1

||u||Hm(Ω) (5)

where μ = min(p, m − 1) and C is a constant that is independent of h, p and u, but depends on m. The

same references show that under certain conditions, such as Laplace’s equation on a domain with reentrant

corners, the exponent on p can be doubled to −2(m − 1), i.e., the p-version of the finite element method

converges twice as fast as the h-version.

With a suitably chosen hp mesh, and other typical assumptions, the error can be shown [14] to converge

exponentially in the number of degrees of freedom,

||ehp||H1(Ω) ≤ C1e

−C2N1/3

(6)

for some C1 and C2 > 0 independent of N.

3 hp-Adaptive Refinement Algorithm

One basic form of an hp-adaptive algorithm is given in Figure 1. If the algorithm is run on a parallel

computer, a load balancing step is performed either before or after the coarsening/refinement part of the

algorithm.

There are a number of approaches to each of the steps of the algorithm. In particular:

4
begin with a very coarse grid

form and solve the linear system

repeat

determine which elements to coarsen and whether to coarsen by h or p

coarsen elements

repeat

determine which elements to refine and whether to refine by h or p

refine elements

until some criterion on amount of refinement is met

form and solve the linear system

until some termination criterion is met

Figure 1: Basic form of an hp-adaptive algorithm.

• How is an element h-refined?

• How is an element p-refined?

• What error indicator is used to guide adaptive refinement?

• When is the program terminated?

• How is an element coarsened?

• How do you determine which elements should be coarsened?

• How do you determine which elements should be refined?

• How much refinement should occur before the linear system is formed and solved again?

• Should an element be refined by h or p?

Other considerations, that are beyond the scope of this paper, include how to create the initial grid, and

how to solve the linear system.

Complete coverage of the possible answers to these questions is beyond the scope of this paper. We

will focus on the choices used for the results given in Section 5, and in some cases briefly mention other

possibilities or give a reference, but this is not intended to be exhaustive. Note that some of the hp strategies

in Section 4 require a different choice, or even a modification of the basic algorithm. These exceptions will

be noted in Section 4.

There are several ways to refine triangles [19]. In this paper, the newest node bisection method [20] is

used. Briefly, a parent triangle is h-refined by connecting one of the vertices to the midpoint of the opposite

side to form two new child triangles. The most recently created vertex is chosen as the vertex to use in this

bisection. Triangles are always refined in pairs (except when the edge to be refined is on the boundary) to

maintain compatibility of the grid. This may require first refining a neighbor triangle to create the second

triangle of the pair. The h-refinement level, li, of a triangle Tiis one more than the h-refinement level of

the parent, with level 0 assigned to the triangles of the initial coarse grid. p-refinement is fairly universally

accepted as increasing the degree of the element by one, followed by enforcing either the minimum rule or

maximum rule for the edges. We will use the minimum rule.

5
Adaptive refinement is guided by a local a posteriori error indicator computed for each element. There

are several choices of error indicators; see for example [2, 34]. For this paper, the error indicator for element

Tiis given by solving a local Neumann residual problem:

Lei = f − Luhp in Ti (7)

ei = 0 on ∂Ti ∩ ∂ΩD (8)

Bei = gN − Buhp on ∂Ti ∩ ∂ΩN (9)

Bei = −

1

2



∂uhp

∂n 

on (∂Ti \ ∂ΩD) \ ∂ΩN (10)

where L, B, f, gN , ∂ΩD, and ∂ΩN are defined in Equations 1-3, h

∂uhp

∂n i

is the jump in the outward normal

derivative of uhp across the element boundary, including the coefficients of the natural boundary conditions,

and in Equation 10 B is modified by setting c(x, y) = 0. If the degree of Tiis pi, the approximate solution,

ei,hp of Equations 7-10 is computed using the hierarchical bases of exact degree pi + 1. The error indicator

for element Tiis then given by

ηi = ||ei,hp||E(Ti)

A global energy norm error estimate is given by

η =

 X

NT

i=1

η

2

i

!1/2

.

One criterion for program termination is that η be smaller than some prescribed error tolerance τ , or,

to base it on the relative error rather than the absolute error, η < τ ||uhp||E(Ω). Other possibilities are

to terminate when some quantity, such as number of elements, number of degrees of freedom, amount of

memory, amount of computation time, etc., is reached, or combinations of criteria. In this paper, the primary

termination criterion is a relative error tolerance, with number of degrees of freedom as a secondary criterion.

Coarsening of elements may be performed to reverse bad decisions about what refinements to perform,

or to allow the grid to follow the behavior of the solution in a time dependent problem. Elements are

h-coarsened by reversing the h-refinement, i.e., joining the child triangles back together to form the parent

triangle. p-coarsening means decreasing the degree of the element by one, and enforcing the minimum or

maximum rule for the edges. For steady state problems, one choice of which elements to coarsen is the

empty set, i.e., don’t perform coarsening. Other than that choice, the most common approach is to coarsen

elements that have a sufficiently small error indicator, subject to any requirements for compatibility of the

grid. In the numerical results of this paper, an element is coarsened if ηi < maxi ηi/100. The value 100 is

arbitrary.

The elements that are refined are usually those that have a sufficiently large error indicator. Perhaps the

most common approach is to refine those with an error indicator that is larger than some fraction, typically

between 1/4 and 1/2, of the maximum error indicator. Another approach, which is used in this paper, is

to refine those with ηi > τ ||uhp||E(Ω)/

√

NT . Note that if every element had ηi = τ ||uhp||E(Ω)/

√

NT then

η/||uhp||E(Ω) = τ , hence the √

NT factor.

There are many ways to determine how much refinement to do before forming and solving the linear

system. One could refine until the global error estimate has been reduced by some factor, such as 1/2

or 1/4, or one could refine until some quantity, e.g. number of elements or degrees of freedom, has been

increased by some factor, such as 2 or 4. Both of these require that reasonable error indicators can be

6
computed on the child elements. The approach taken in this paper is to perform the refine loop once. The

downside of this approach is that it requires more passes through the outer loop, which means forming

and solving the linear system more times. But for the purpose of this paper, which is to determine the

convergence rate of various hp-adaptive strategies with respect to number of degrees of freedom, the excess

computation time is not important.

The method for determining whether an element should be refined by h or by p is called an hp-adaptive

strategy. Several strategies have been proposed over the years. Many of them will be described in the next

section.

4 The hp-Adaptive Strategies

In this section, the hp-adaptive strategies that have been proposed in the literature are presented. In some

cases, these strategies were developed in the context of 1D problems, rectangular elements, or other settings

that are not fully compatible with the context of this paper. In those cases, the strategy is appropriately

modified for 2D elliptic PDEs and newest node bisection of triangles.

4.1 Use of a priori Knowledge of Solution Regularity

It is well known that for smooth solutions p-refinement will produce an exponential rate of convergence, but

near singularities p-refinement is less effective than h-refinement. This is a consequence of the a priori error

bound in Equation 5. For this reason, many of the hp strategies use h-refinement in areas where the solution

is irregular (i.e., locally fails to be in Hm for some finite m, also called nonsmooth) or nearly irregular,

and p-refinement elsewhere. The simplest strategy is to use any a priori knowledge about irregularities. For

example, it is known that linear elliptic PDEs with smooth coefficients and piecewise analytic boundary data

will have point singularities only near reentrant corners of the boundary and where boundary conditions

change [4]. Another example would be a situation where one knows the approximate location of a shock in

the interior of the domain.

An hp-adaptive strategy of this type was presented by Ainsworth and Senior [4]. In this approach they

simply flag vertices in the initial mesh as being possible trouble spots. During refinement an element is

refined by h if it contains a vertex that is so flagged, and by p otherwise. We will refer to this strategy by

the name APRIORI.

We extend this strategy to allow more general regions of irregularity, and to provide the strength of the

irregularity. The user provides a function that, given an element Ti as input, returns a regularity value for

that element. For true singularities, it would ideally return the maximum value of m such that u ∈ Hm(Ti).

But it can also indicate that a triangle intersects an area that is considered to be nearly irregular, like a

boundary layer or sharp wave front. Based on the definition of μ in Equation 5, if the current degree of the

triangle is pi and the returned regularity value is mi, we do p-refinement if pi ≤ mi − 1 and h-refinement

otherwise. The same approach is used in all the following strategies that estimate the local regularity mi.

4.2 Estimate Regularity Using Smaller p Estimates

S ̈uli, Houston and Schwab [32] presented a strategy based on Equation 5 and an estimate of the convergence

rate in p using error estimates based on pi − 2 and pi − 1. We will refer to this strategy as PRIOR2P. This

requires pi ≥ 3, so we always use p-refinement in elements of degree 1 and 2.

7
Suppose the error estimate in Equation 5 holds on individual elements and that the inequality is an

approximate equality. Let ηi,pi−2 and ηi,pi−1 be a posteriori error estimates for partial approximate solutions

over triangle Ti using the bases up to degree pi − 2 and pi − 1, respectively. Then

ηi,pi−1

ηi,pi−2

≈



pi − 1

pi − 2

−(mi−1)

and thus the regularity is estimated by

mi ≈ 1 −

log(ηi,pi−1/ηi,pi−2)

log((pi − 1)/(pi − 2))

Use p-refinement if pi ≤ mi − 1 and h-refinement otherwise.

Thanks to the p-hierarchical basis, the computation of the error estimates is very inexpensive. For 1 ≤

j < pi,

uhp|Ti =

X

supp(φk)∩Ti6=∅

αkφk =

X

supp(φk)∩Ti6=∅

deg(φk)≤pi−j

αkφk +

X

supp(φk)∩Ti6=∅

deg(φk)>pi−j

αkφk

where supp(φk) is the support of φk and deg(φk) is the degree of φk. The last sum is the amount by which

the solution changed when the degree of the element was increased from pi−j to pi, and provides an estimate

of the error in the partial approximate solution of degree pi − j given in the next to last sum. (Indeed, the

local Neumann error estimator of Equations 7-10 approximates this quantity for the increase from degree pi

to pi + 1.) Thus the error estimates are

ηi,pi−j = || X

supp(φk)∩Ti6=∅

deg(φk)>pi−j

αkφk||H1(Ti)

which only involves computing the norm of known quantities.

4.3 Type parameter

Gui and Babuˇska [13] presented an hp-adaptive strategy using what they call a type parameter, γ. This

strategy is also used by Adjerid, Aiffa and Flaherty [1]. We will refer to this strategy as TYPEPARAM.

Given the error estimates ηi,pi and ηi,pi−1, define

R(Ti) = ( ηi,pi

ηi,pi−1

ηi,pi−1 6= 0

0 ηi,pi−1 = 0

By convention, ηi,0 = 0, which forces p-refinement if pi = 1.

R is used to assess the perceived solution smoothness. Given the type parameter, 0 ≤ γ < ∞, element

Tiis said to be of h-type if R(Ti) > γ, and of p-type if R(Ti) ≤ γ. If element Tiis selected for refinement,

then refine it by h-refinement if it is of h-type and p-refinement if it is of p-type. Note that γ = 0 gives pure

h-refinement and γ = ∞ gives pure p-refinement.

For the error estimates, we use the local Neumann error estimate of Equations 7-10 for ηi,pi, and the

ηi,pi−1 of Section 4.2. For the results of Section 5, we use γ = 0.3 if the solution has a singularity, and

γ = 0.6 otherwise. 1

1The value for this parameter, and the parameters of the other strategies, was determined by a preliminary experiment to

determine a single value (or possibly two values dependent on singularness) that generally works best, using a subset of the

test problems.

8
4.4 Estimate Regularity Using Larger p Estimates

Another approach that estimates the regularity is given by Ainsworth and Senior [3]. This strategy uses

three error estimates based on spaces of degree pi + 1, pi + 2 and pi + 3, so we refer to it as NEXT3P.

The error estimate used to approximate the regularity is a variation on the local Neumann residual error

estimate given by Equations 7-10 in which Equation 10 is replaced by

Bei = gi on (∂Ti \ ∂ΩD) \ ∂ΩN

where giis an approximation of Bu that satisfies an equilibrium condition. This is the equilibrated residual

error estimator in [2].

The local problem is solved on element Ti three times using the spaces of degree pi + q, q = 1, 2, 3, to

obtain error estimates ei,q. In contrast to the local Neumann residual error estimate, the whole space over

Tiis used, not just the p-hierarchical bases of degree greater than pi. These approximations to the error

converge to the true solution of the residual problem at the same rate the approximate solution converges

to the true solution of Equations 1-3, i.e.

||ei − ei,q||E(Ti) ≈ C(pi + q)

−α

where C and α are positive constants that are independent of q but depend on Ti. Using the Galerkin

orthogonality

||ei − ei,q||2

E(Ti) = ||ei

||2

E(Ti) − ||ei,q||2E(Ti)

this can be rewritten

||ei||2

E(Ti) − ||ei,q||2E(Ti) ≈ C

2

(pi + q)

−2α

.

We can compute ||ei,q||2

E(Ti)

and pi + q for q = 1, 2, 3 from the approximate solutions, so the three constants

||ei||E(Ti), C and α can be approximated by fitting the data. Then, using the a priori error estimate in

Equation 5, the approximation of the local regularity is mi = 1 + α. Use p-refinement if pi ≤ mi − 1 and

h-refinement otherwise.

4.5 Texas 3 Step

The Texas 3 Step strategy [8, 23, 24] first performs h-refinement to get an intermediate grid, and follows

that with p-refinement to reduce the error to some given error tolerance, τ . We will refer to this strategy as

T3S. Note that for this strategy the basic form of the hp-adaptive algorithm is different than that in Figure

1.

The first step is to create an initial mesh with uniform p and nearly uniform h such that the solution is in

the asymptotic range of convergence in h. This may be accomplished by performing uniform h-refinements

of some very coarse initial mesh until the asymptotic range is reached. The resulting grid has N0 elements

with sizes hi, degrees pi and a posteriori error estimates ηi, and approximate solution u0. The results in

Section 5 begin with p = 1 and assume the initial grid is sufficiently fine in h.

The second step is to perform adaptive h-refinement to reach an intermediate error tolerance γτ where γ

is a given parameter. In the references, γ is in the range 5 − 10, usually 6 in the numerical results. This

intermediate grid is created by computing a desired number of children for each element Ti by the formula

ni =

 

Λ

2

i NIh

2μi

i

p

2(mi−1)

i

η

2

I

! 1

βμi+1

(11)

9
where NI =

Pni

is the number of elements in the intermediate grid, miis the local regularity of the solution,

μi = min(pi, mi − 1), ηI = γτ ||u0||E, β = 1 for 2D problems, η

2

0 =

Pη

2

i

and

Λi =

ηiΛ

η0

where

Λ = η0p

mi−1

i

h

μi

i

See any of the above references for the derivation of this formula. It is based on the a priori error estimate

in Equation 5. Inserting the expression for Λiinto Equation 11 and using β = 1 we arrive at

ni =



η

2

i NI

η

2

I

 1

μi+1

NI is not known at this point, since it is the sum of the ni. Successive iterations are used to solve for ni and

NI simultaneously. We use 5 iterations, which preliminary experiments showed to be sufficient (convergence

was usually achieved in 3 or 4 iterations). Once the ni have been determined, we perform ⌊0.5 + log2 ni⌋

uniform h-refinements (bisections) of each element Ti to generate approximately ni children, and solve the

discrete problem on the intermediate grid.

The third step is to perform adaptive p-refinement to reduce the error to the desired tolerance τ . The

new degree for each element is given by

pˆi = pi



ηI,i√NI

ηT

 1

mi−1

where ηI,i is the a posteriori error estimate for element Ti of the intermediate grid and ηT = τ ||u0||E. Again,

the formula is a simple reduction of the equations derived in the references. p-refinement is performed to

increase the degree of each element Ti to ˆpi, and the discrete problem is solved on the final grid.

In the results of Section 5, if ni < 2 or ˆpi < pi then refinement is not performed. Also, to avoid excessive

refinement, the number of h-refinements done to any element in step 2 and number of p-refinements in step

3 is limited to 3.

The strategy of performing all the h-refinement in one step and all the p-refinement in one step is adequate

for low accuracy solutions (e.g. 1%), but is not likely to work well with high accuracy solution (e.g. 10−8

relative error) [25]. We extend the Texas 3 Step strategy to high accuracy by cycling through steps 2 and 3

until the final tolerance τfinal is met. τ in the algorithm above is now the factor by which one cycle of steps

2 and 3 should reduce the error. Toward this end, before step 2 the error estimate η0 is computed for the

current grid. The final (for this cycle) and intermediate targets are now given by ηT = τη0 and ηI = γηT .

In the results of Section 5 we use τ = 0.1 and γ = 6. For the local regularity mi we use the same routine as

the APRIORI strategy (Section 4.1).

4.6 Alternate h and p

This strategy, which will be referred to as ALTERNATE, is a variation on T3S that is more like the algorithm

of Figure 1. The difference from T3S is that instead of predicting the number of refinements needed to reduce

the error to the next target, the usual adaptive refinement is performed until the target is reached. Thus in

10
step 2 all elements with an error indicator larger than ηI /

√

N0 are h-refined. The discrete problem is solved

and the new error estimate compared to ηI . This is repeated until the error estimate is smaller than ηI .

Step 3 is similar except adaptive p-refinement is performed and the target is ηT . Steps 2 and 3 are repeated

until the final error tolerance is achieved.

4.7 Nonlinear Programming

Patra and Gupta [26] proposed a strategy for hp mesh design using nonlinear programming. We refer to

this strategy as NLP. They presented it in the context of quadrilateral elements with one level of hanging

nodes, i.e., an element edge is allowed to have at most one hanging node. Here it is modified slightly for

newest node bisection of triangles with no hanging nodes. This is another approach that does not strictly

follow the algorithm in Figure 1.

Given a current grid with triangles {Ti}, degrees {pi}, h-refinement levels {li}, error estimates {ηi}, and

element diameters

hi =



1

√

2

li

H0,i

where H0,i is the diameter of the element in the initial grid that contains Ti, the object is to determine new

mesh parameters {pˆi} and {

ˆli}, i = 1..NT , by solving an optimization problem. The new grid is obtained

by refining Ti

ˆli − li times (or coarsening if ˆli < li) and assigning degree ˆpi to the 2ˆli−li children. The size

of the children of Tiis

hˆ

i =



1

√

2

ˆli

H0,i.

There are two forms of the optimization problem, which can be informally stated as 1) minimize the

number of degrees of freedom (or some other measure of grid size) subject to the error being less than a

given tolerance and other constraints, and 2) minimize the error subject to the number of degrees of freedom

being less than a given limit and other constraints. We will only consider the first form here; the second

form simply reverses the objective function and constraint.

Computationally, the square of the error is approximated by PNT

i=0 ηˆ

2

i where ˆηi

, to be defined later, is an

estimate of the error in the refined grid over the region covered by Ti. The number of degrees of freedom

associated with a triangle of degree p is taken to be 3/6 (one for each vertex with an average of six triangles

sharing a vertex) plus 3(p−1)/2 (p−1 for each edge with two triangles sharing an edge) plus (p−1)(p−2)/2

(for the interior), which is p

2/2. Thus the number of degrees of freedom over the children of Ti

is 2ˆli−li pˆ

2

i

/2.

11
We can now formally state the optimization problem as

minimize

{

ˆli}, {pˆi}

X

NT

i=1

2

ˆli−li

pˆ

2

i

2

(12)

s.t.

X

NT

i=1

ηˆ

2

i < τˆ

2

(13)

ˆlj − 1 ≤ ˆli ≤ ˆlj + 1 ∀j such that Tj shares an edge with Ti (14)

0 ≤ ˆli ≤ lmax (15)

1 ≤ pˆi ≤ pmax (16)

li − ∆ldec ≤ ˆli ≤ li + ∆linc (17)

pi − ∆pdec ≤ pˆi ≤ pi + ∆pinc (18)

where ˆτ is the error tolerance for this refinement phase. We use ˆτ = η/4 where η is the global error estimate

on the current grid. The divisor 4 is arbitrary and could be replaced by some other value. In practice,

Equation 13 is divided through by τ

2

so that the numbers are O(1). Equation 14 is a necessary condition

for compatibility of the grid (in [26] it enforces one level of hanging nodes). It is not a sufficient condition,

however any violations of compatibility while this condition is met are cases where only one triangle of a

compatibly divisible pair was refined, and it is a slight adjustment to the optimal solution to also refine the

other one to maintain compatibility. Equation 15 insures that coarsening does not go beyond the initial grid,

and that the refinement level of an element does not exceed a prescribed limit lmax. Similarly, Equation 16

insures that element degrees do not go below one or exceed a prescribed limit pmax. Also, because many

quantities are only approximate, it is wise to limit the amount of change that occurs to any element during

one phase of refinement. Equations 17 and 18 restrict the amount of change that can occur at one time, i.e.,

restrict the amount of decrease in l and p to prescribed limits ∆ldec and ∆pdec, and the amount of increase

to ∆linc and ∆pinc. In the results in Section 5 we used ∆ldec = 1, ∆pdec = 1, ∆linc = 3, and ∆pinc = 1.

Since the ˆli and ˆpi are naturally integers, the optimization problem is a mixed integer nonlinear program,

which is known to be NP-hard. To make the problem tractable, the integer requirement is dropped to give

a nonlinear program which can be solved by one of several software packages. For the results in Section 5,

we used the program ALGENCAN 2 Version 2.2.1 [5, 9]. Following solution of the nonlinear program, the

ˆli and ˆpi are rounded to the nearest integer.

It remains to define ˆηi, the estimate of the error in the refined grid over the region covered by Ti. Assuming

approximate equality in the a priori error estimate of Equation 5, we have

ηi ≈ C

h

μi

i

p

mi−1

i

||u||Hm(Ti)

and

ηˆi ≈ C

hˆμi

i

pˆ

mi−1

i

||u||Hm(Ti)

2The mention of specific products, trademarks, or brand names is for purposes of identification only. Such mention is not to

be interpreted in any way as an endorsement or certification of such products or brands by the National Institute of Standards

and Technology. All trademarks mentioned herein belong to their respective owners.

12
where mi

is the local regularity over Ti and μi = min(pi, mi − 1). Combining these leads to

ηˆi ≈

hˆμi

i

pˆ

mi−1

i

p

mi−1

i

h

μi

i

ηi =



1

√

2

μi(ˆli−li) 

pi

pˆi

mi−1

ηi

and thus the constraint in Equation 13 is

X

NT

i=1



1

2

min(pi,mi−1)(ˆli−li) 

pi

pˆi

2(mi−1)

η

2

i < τˆ

2

in which the only remaining quantity to be determined is mi. Patra and Gupta suggest estimating mi by

using the observed convergence rate from two grids, with a formula very similar to that used in the PRIOR2P

strategy of Section 4.2, so we use the same estimate as PRIOR2P.

4.8 Another Optimization Strategy

Another strategy based on the formulation and solution of an optimization problem is given in Novotny

et al. [22]. However, it turns out that 1) the optimization does not work near singularities, so a priori

knowledge of singularities must be used to force h-refinement near singularities, and 2) for the finite element

method and class of problems considered in this paper, the strategy always chooses p-refinement except for

extremely large elements. Thus, this strategy is (nearly) identical to the APRIORI strategy, and will not be

considered further in this paper.

4.9 Predict Error Estimate on Assumption of Smoothness

Melenk and Wohlmuth [17] proposed a strategy based on a prediction of what the error should be if the

solution is smooth. We call this strategy SMOOTH PRED.

When refining element Ti, assume the solution is locally smooth and that the optimal convergence rate is

obtained. If h-refinement is performed and the degree of Tiis pi, then the expected error on the two children

of Tiis reduced by a factor of √

2

pi

as indicated by the a priori error estimate of Equation 5. Thus if ηi

is the error estimate for Ti, predict the error estimate of the children to be γhηi/

√

2

pi

where γh is a user

specified parameter. If p-refinement is performed on Ti, exponential convergence is expected, so the error

should be reduced by some constant factor γp ∈ (0, 1), i.e., the predicted error estimate is γpηi. When the

actual error estimate of a child becomes available, it is compared to the predicted error estimate. If the

error estimate is less than or equal to the predicted error estimate, then p-refinement is indicated for the

child. Otherwise, h-refinement is indicated since presumably the assumption of smoothness was wrong. For

the results in Section 5 we use γh = 2 and γp =

√

0.4.

4.10 Larger of h-Based and p-Based Error Indicators

In 1D, Schmidt and Siebert [28] proposed a strategy that uses two a posteriori error estimates to predict

whether h-refinement or p-refinement will reduce the error more. We extend this strategy to bisected triangles

and refer to it as H&P ERREST.

The local Neumann residual error estimate given by Equations 7-10 is actually an estimate of how much

the norm of the solution will change if Tiis p-refined. This is because the solution of the local problem is

estimated using the p-hierarchical bases that would be added if Tiis p-refined, so it is an estimate of the

13
actual change that would occur. Using the fact that the current space is a subspace of the refined space and

Galerkin orthogonality, it can be shown that

||u − uˆhp||2 = ||u − uhp||2 − ||uˆhp − uhp||2

where ˆuhp is the solution in the refined space. Thus the change in the solution indicates how much the error

will be reduced.

A second error estimate for Ti can be computed by solving a local Dirichlet problem

Lei = f − Luhp in Ti ∪ T

mate

i

(19)

ei = gD − uhp on ∂(Ti ∪ T

mate

i

) ∩ ∂ΩD (20)

Bei = gN − Buhp on ∂(Ti ∪ T

mate

i

) ∩ ∂ΩN (21)

ei = 0 on ∂(Ti ∪ T

mate

i

) \ ∂ΩD



\ ∂ΩN (22)

where T

mate

i

is the element that is refined along with Tiin the newest node bisection method [20]. The

solution to this problem is approximated by an h-refinement of the two elements using only the new basis

functions. The error estimate obtained by taking the norm of this approximate solution is actually an

estimate of how much the solution will change, or the error will be reduced, if h-refinement is performed.

Schmidt and Siebert divide the two error estimates by the associated increase in the number of degrees

of freedom to obtain an approximate error reduction per degree of freedom. In addition or instead, one

of the error estimates can be multiplied by a user specified constant to bias the refinement toward h- or

p-refinement. In the results of Section 5 the p-based error estimate is multiplied by 2.

The type of refinement that is used is the one that corresponds to the larger of the two modified error

estimates.

4.11 Legendre coefficient strategies

There are three hp-adaptive strategies that are based on the coefficients in an expansion of the solution

in Legendre polynomials. In one dimension, the approximate solution in element Ti with degree pi can be

written

ui(x) = Xpi

j=0

ajPj (x)

where Pj is the j

th degree Legendre polynomial scaled to the interval of element Ti

.

Mavriplis [16] estimates the decay rate of the coefficients by a least squares fit of the the last four coefficients

aj to Ce−σj . Elements are refined by p-refinement where σ > 1 and by h-refinement where σ ≤ 1. We refer

to this strategy as COEF DECAY. When four coefficients are not available, we fit to whatever is available.

If only one coefficient is available, we use p-refinement.

Houston et al. [15] present the other two approaches which use the Legendre coefficients to estimate the

regularity of the solution. One approach estimates the regularity using the root test yielding

mi =

log 

2pi+1

2a2

pi



2 log pi

.

If pi = 1, use p-refinement. Otherwise, use p-refinement if pi ≤ mi − 1 and h-refinement if pi > mi − 1. We

refer to this strategy as COEF ROOT.

14
They also present a second way of estimating the regularity from the Legendre coefficients using the ratio

test. However, they determined the ratio test is inferior to the root test, so it will not be considered further

in this paper.

Both Mavriplis and Houston et al. presented the strategies in the context of one dimension and use the

Legendre polynomials as the local basis so the coefficients are readily available. In [15] it is extended to 2D

for rectangular elements with a tensor product of Legendre polynomials, and the regularity is estimated in

each dimension separately, so the coefficients are still readily available. Eibner and Melenk [12] extended the

COEF DECAY strategy to quadrisected triangles with an orthogonal polynomial basis. In this study we are

using triangular elements which have a basis that is based on Legendre polynomials [33]. In this basis there

are 3 + max(j − 2, 0) basis functions of exact degree j over an element, so we don’t have a single Legendre

polynomial coefficient to use. Instead, for the coefficients aj we use the l1 norm of the coefficients of the

degree j basis functions, i.e.

aj =

X

k s.t. deg(φk)=j

supp(φk)∩Ti6=∅

|αk|

4.12 Reference Solution Strategies

Demkowicz and his collaborators developed an hp-adaptive strategy over a number of years, presented in

several papers and books, e.g. [10, 11, 27, 31]. In its full glory, the strategy is quite complicated. Here

we present only the basic ideas of the algorithm and how we have adapted it for bisected triangles (it is

usually presented in the context of rectangular elements with some reference to quadrisection triangles), and

refer to the references for further details. We refer to this strategy as REFSOLN EDGE because it relies on

computing a reference solution and bases the refinement decisions on edge refinements. Note that for this

strategy the basic form of the hp-adaptive algorithm is different than that in Figure 1.

The algorithm is first presented for 1D elliptic problems. Given the current existing (coarse) mesh,

Gh,p := Ghp, and current solution, uh,p := uhp, a uniform refinement in both h and p is performed to

obtain a fine mesh Gh/2,p+1. The equation is solved on the fine mesh to obtain a reference solution uh/2,p+1.

The norm of the difference between the current solution and reference solution is used as the global error

estimate, i.e.,

η = ||uh/2,p+1 − uh,p||H1

The next step is to determine the optimal refinement of each element. This is done by considering a

p-refinement and all possible (bisection) h-refinements (i.e., all possible assignments of p to the two children

of an h-refinement) that give the same increase in the number of degrees of freedom as the p-refinement.

In 1D, this means that the sum of the degrees of the two children must be p + 1, resulting in a total of p

h-refinements and one p-refinement to be examined. For each possibility, the error decrease rate is computed

as

|uh/2,p+1 − Πhp,iuh/2,p+1|

2

H1(Ti) − |uh/2,p+1 − Πnew,iuh/2,p+1|

2

H1(Ti)

Nnew − Nhp

where Πhp,iuh/2,p+1 is the projection-based interpolant of the reference solution in element Ti, computed

by solving a local Dirichlet problem, and Πnew,i is the projection onto the resulting elements from any one

of the candidate refinements. The refinement with the largest error decrease rate is selected as the optimal

refinement. In the case of h-refinement, the degrees may be increased further by a process known as following

the biggest subelement error refinement path, which is also used to determine the guaranteed element rate;

see [10] for details.

15
Elements that have a guaranteed rate larger than 1/3 the maximum guaranteed rate are selected for

refinement; the factor 1/3 is arbitrary.

The 2D algorithm also begins by computing a reference solution on the globally hp-refined grid Gh/2,p+1.

(For bisected triangles, we should use the subscript h/√

2, p + 1 for the fine grid and solution, but for

simplicity we will use the original notation.) Then for each edge in the grid, the choice between p- and

h-refinement, the determination of the guaranteed edge rate, and the selection of edges to refine are done

exactly as in 1D, except that a weighted H1seminorm is used instead of the more natural H1/2seminorm

which is difficult to work with. In the case of bisected triangles, we only consider edges that would be refined

by the bisection of an existing triangle.

The h-refinement of edges determines the h-refinement of elements. It remains to determine the degree of

each element. As a starting point, element degrees are assigned to satisfy the minimum rule for edge degrees,

using the edge degrees determined in the previous step. Then the biggest subelement error refinement path

is followed to determine the guaranteed element rate and assignment of element degrees. We again refer

to [10] for details. Finally, the minimum rule for edge degrees is enforced by increasing edge degrees as

necessary.

A related, but simpler, approach was developed by Sol ́ın et al. [30]. We refer to this strategy as REF- ˇ

SOLN ELEM since it also begins by computing a reference solution, uh/2,p+1, on Gh/2,p+1, but bases the

refinement on elements. The basic form of the hp-adaptive algorithm is different than that in Figure 1 for

this strategy, also.

The local error estimate is given by the norm of the difference between the reference solution and the

current solution,

ηi = ||uh/2,p+1 − uh,p||H1(Ti)

and the elements with the largest error estimates are refined. If Tiis selected for refinement, let p0 =

⌊(pi + 1)/2⌋ and consider the following options:

• p-refine Ti to degree pi + 1,

• p-refine Ti to degree pi + 2,

• h-refine Ti and consider all combinations of degrees p0, p0 + 1 and p0 + 2 in the children.

In all cases the minimum rule is used to determine edge degrees. In [30], quadrisection of triangles is used

leading to 83 options to consider. With bisection of triangles, there are only 11 options. Also, since the object

of dividing by two to get p0 is to make the increase in degrees of freedom from h-refinement comparable to

that of p-refinement, we use p0 = ⌊(pi + 1)/

√

2⌋ since there are only two children instead of four. Solin et al.

allow an unlimited number of hanging nodes, so they have no issue of how to assign the degrees of children

that were created to maintain compatibility or one level of hanging nodes. For the newest node bisection of

triangles algorithm, we assign ⌊(p + 1)/

√

2⌋ to both children of a triangle of degree p that is refined only for

the sake of compatibility.

For each candidate, the standard H1 projection ΠH1

(Ti)

candidate of uh/2,p+1 onto the corresponding space is

performed, and the projection error in the H1 norm, ζcandidate, is computed,

ζcandidate = ||uh/2,p+1 − Π

H1(Ti)

candidateuh/2,p+1||H1(Ti)

as well as the projection error of the projection onto Ti

, ζi.

The selection of which candidate to use is not simply the candidate with the smallest projection error

[29]. Let Ni be the number of degrees of freedom in the space corresponding to Ti, and Ncandidate the

16
number of degrees of freedom in the space corresponding to a candidate. For simplicity, when computing Ni

and Ncandidate we apply the minimum rule for edge degree ignoring the degrees of the neighbors of Ti, e.g.

Ni = (pi + 1)(pi + 2)/2 regardless of what the actual edge degrees of Ti are.

Candidates with ζcandidate > ζi are discarded. We also discard any of the h-refined candidates for which

the degrees are both greater than pi since the reference solution is (locally) in that space. Let n be the

number of remaining candidates. Compute the average and standard deviation of the base 10 logarithms of

the ζ’s

 ̄ζ =

1

n

X

candidates

log ζcandidate

σ =

s

1

n

X

candidates

(log ζcandidate)

2 −  ̄ζ2

Finally, to determine which candidate to use, select an above-average candidate with the steepest error

decrease, i.e., from among the candidates with log ζcandidate <  ̄ζ +σ and Ncandidate > Ni, select the candidate

that maximizes

log ζi − log ζcandidate

Ncandidate − Ni

(23)

Following the refinement that is indicated by the selected candidate, the minimum rule for edge degrees is

applied.

This algorithm can be modified slightly to bias the refinement towards or away from p refinement to

improve the performance. Given a parameter pbias, multiply the value from Equation 23 by it for all the

p-refinement candidates. pbias > 1 will bias the refinement toward doing p-refinement, and pbias < 1 will bias

the refinement toward doing h-refinement. For the results in Section 5 we use pbias = 2 for most problems,

and pbias = 4 for the analytic, mild wave front and both peak problems, which are the easiest problems.

5 Numerical Results

This section contains the results of a numerical experiment to compare the hp-adaptive strategies’ performance on a suite of 21 test problems with various difficulties that adaptive refinement should locate. The

primary criteria for comparing the strategies is the convergence of the relative error in the energy norm as a

function of the number of degrees of freedom, N. The results for each problem are given in Sections 5.1-5.21,

and summary results for comparison of the strategies are given in Section 5.23. We also give some indication

of the relative amount of time required to obtain the solution in Section 5.22.

The full details of the test problems can be found in a separate report [21]. Here we just give a brief

description of each problem and an image of the solution, both as a color map and as a surface in perspective.

Recall that Poisson’s equation is uxx+uyy = f(x, y) and Laplace’s equation is Poisson’s equation with f = 0.

Each problem is solved with each hp strategy using the hp-adaptive algorithm of Section 3, except for

those strategies that dictate using a variation on that algorithm, as indicated in Section 4. To examine

the convergence of the error as a function of N, each problem is solved using each strategy several times

with different values of the termination tolerance τ . The relative energy norm of the error and N are

recorded at the end of each run to give a set of points for the convergence data. In most cases we used

τ = 0.1, 0.05, 0.02, 0.01, 0.005 . . . 2x10−8, 10−8, although some of the more difficult problems required

ending the sequence earlier.

17
Figure 2: The initial grid for problems on square domains.

The initial grid for problems on a square domain is shown in Figure 2. The initial grid for the reentrant

corner problems is obtained by removing the unneeded elements from the grid in Figure 2. The initial grid

for the battery problem is shown in Section 5.11.

In the following subsections for each problem, we present the following results of the computations.

We begin with a sample grid for each strategy, to show the wide variation in the different strategies’ choice

between h and p refinement. In all of the grid images, the color indicates the degree of the polynomial over

each element. To obtain the grid, we pick one particular value of the termination relative error tolerance τ

and run each strategy to that tolerance. In cases where there is strong h-refinement in a small area we also

zoom in on that area to show the detail at the fine level.

Second we present a plot of N vs. the error on a log-log scale. These graphs have a curvature indicating the

exponential rate of convergence. The black circles and connecting lines show the convergence data obtained

by solving the problem with a sequence of termination tolerances. Points that were obvious outliers were

omitted. The red and green curves are exponential least squares fits to the data. According to Equation 6

the error should converge like AeBN1/3. The red curve is a least squares fit to this form. As will be seen,

this fit is not always close to the data. Often the data exhibit exponential convergence, but with a different

exponent on N than 1/3. The green curve is a least squares fit to the form AeBNC. This 3-parameter least

squares fit will be the primary means of comparing the performance of the strategies.

Following the individual strategy convergence plots is a composite plot containing the 3-parameter least

squares fit curves of all strategies on a single graph.

Some papers on hp-adaptive refinement present the convergence plots using a cube root of N vs. logarithm

of error scale. This is because, if the error converges like AeBN1/3, then the convergence plot will be a straight

line using this scale. To illustrate this, we present the cube root vs. log plots for one problem, the L-shaped

domain problem (Section 5.4), along with the 2-parameter least squares fit.

The parameters obtained by the 3-parameter and 2-parameter least squares fits are given in tables. In

the 3-parameter fit, C (the power on N, theoretically 1/3) indicates the curvature of the curve on a log-log

plot. Very small values indicate the exponential nature of the convergence is weak. Larger values indicate a

larger curvature, which asymptotically gives faster convergence rates. In the 2-parameter fit, B is the slope

of the line on the cube root vs. log convergence plot. Strategies with smaller values of B (larger magnitude,

since B is negative) will have steeper slopes, and asymptotically be the better strategies.

18
Figure 3: Computation of the factor by which N for a particular strategy is larger than N for the best

strategy. In this illustration, for an accuracy of 10−6the factor for ALTERNATE is 53730/7787 ≈ 6.90.

The performance of the strategies are compared on each problem at two accuracy requirements. For low

accuracy, which is typical in engineering applications, we use 10−2, or 1% relative error, for most problems.

For high accuracy, which is of interest mathematically and useful in some scientific applications, we use 10−6

for most problems.

To compare the strategies, consider the 3-parameter least squares fit. For each strategy, compute the

value of N that gives the desired accuracy according to the formula for the 3-parameter least squares fit,

as illustrated in Figure 3. Let Nbest be the minimum such value over all the strategies. For each strategy

compute the factor by which N is larger than the best strategy, Nstrategy/Nbest. For example, in Figure 3

the factor for ALTERNATE is 53730/7787 ≈ 6.90. The final tables of each subsection contain these factors

at low and high accuracy, with the accuracy requirement given in the caption. The strategies are ordered

by increasing value of the factor, implicitly giving the rank (first, second, etc.) of each strategy.

These computations were performed using the adaptive finite element code PHAML Version 1.8.1 [18]

on a single processor. During the period of this investigation there were changes to the available hardware

and software, but we do not believe any of these changes would effect the outcome of these computations,

except in Section 5.22 where a consistent computational environment is used. The computers were 32-bit

and 64-bit x86-class computers operating under CentOS 5.x distributions of Linux. PHAML was compiled

with the Intel Fortran compiler.

19
Figure 4: The solution of the analytic problem.

5.1 Analytic Solution

The analytic problem in [21] is Poisson’s equation on the unit square with Dirichlet boundary conditions.

The solution is the polynomial

2

4pxp

(1 − x)

p

y

p

(1 − y)

p

with p = 10. 24pis a normalization factor so that the L∞ norm is 1.0. The purpose of this test problem

is to see how the methods perform on a smooth, well-behaved problem that does not really need adaptive

refinement at all. For the grid images we used τ = 10−4. For the APRIORI strategy, we choose to always

refine by p, i.e., it is just p-adaptive refinement.

20
Figure 5: Example grid for the ALTERNATE strategy with the analytic problem.

Figure 6: Example grid for the APRIORI strategy

with the analytic problem.

Figure 7: Example grid for the COEF DECAY strategy with the analytic problem.

Figure 8: Example grid for the COEF ROOT strategy with the analytic problem.

Figure 9: Example grid for the H&P ERREST strategy with the analytic problem.

Figure 10: Example grid for the NEXT3P strategy

with the analytic problem.

21
Figure 11: Example grid for the NLP strategy with

the analytic problem.

Figure 12: Example grid for the PRIOR2P strategy

with the analytic problem.

Figure 13: Example grid for the REFSOLN EDGE

strategy with the analytic problem.

Figure 14: Example grid for the REFSOLN ELEM

strategy with the analytic problem.

Figure 15: Example grid for the SMOOTH PRED

strategy with the analytic problem.

Figure 16: Example grid for the T3S strategy with

the analytic problem.

22
Figure 17: Example grid for the TYPEPARAM strategy with the analytic problem.

Figure 18: Log-Log plot of the convergence of the

ALTERNATE strategy with the analytic problem.

Figure 19: Log-Log plot of the convergence of the

APRIORI strategy with the analytic problem.

Figure 20: Log-Log plot of the convergence of the

COEF DECAY strategy with the analytic problem.

23
Figure 21: Log-Log plot of the convergence of the

COEF ROOT strategy with the analytic problem.

Figure 22: Log-Log plot of the convergence of the

H&P ERREST strategy with the analytic problem.

Figure 23: Log-Log plot of the convergence of the

NEXT3P strategy with the analytic problem.

Figure 24: Log-Log plot of the convergence of the

NLP strategy with the analytic problem.

24
Figure 25: Log-Log plot of the convergence of the

PRIOR2P strategy with the analytic problem.

Figure 26: Log-Log plot of the convergence of the

REFSOLN EDGE strategy with the analytic problem.

Figure 27: Log-Log plot of the convergence of the

REFSOLN ELEM strategy with the analytic problem.

Figure 28: Log-Log plot of the convergence of the

SMOOTH PRED strategy with the analytic problem.

25
Figure 29: Log-Log plot of the convergence of the

T3S strategy with the analytic problem.

Figure 30: Log-Log plot of the convergence of the

TYPEPARAM strategy with the analytic problem.

26
Figure 31: Log-Log plot of the convergence of all strategies with the analytic problem.

27
strategy A B C

ALTERNATE 139.23 -2.18 0.21

APRIORI 18.38 -0.64 0.38

COEF DECAY 2.48x108-12.68 0.098

COEF ROOT 501.62 -2.81 0.20

H&P ERREST 2.18x1010 -17.82 0.070

NEXT3P 4.96x1034 -69.95 0.030

NLP 9.58x103-3.54 0.19

PRIOR2P 7.83x103-4.91 0.15

REFSOLN EDGE 101.26 -1.49 0.29

REFSOLN ELEM 18.10 -0.82 0.34

SMOOTH PRED 9.57 -0.43 0.40

T3S 9.20x106-7.67 0.13

TYPEPARAM 559.51 -2.04 0.26

Table 1: Parameters of the least squares fit for

||ehp||E = AeBNC

dof for the analytic problem.

strategy factor

REFSOLN EDGE 1.00

NEXT3P 1.01

TYPEPARAM 1.02

APRIORI 1.06

REFSOLN ELEM 1.07

COEF DECAY 1.15

COEF ROOT 1.26

PRIOR2P 1.30

H&P ERREST 1.35

SMOOTH PRED 1.73

ALTERNATE 1.80

NLP 1.86

T3S 2.63

Table 2: Factor by which N is larger than the best

strategy for the analytic problem at low accuracy,

1.0x10−2.

strategy A B

ALTERNATE 0.54 -0.44

APRIORI 107.21 -1.08

COEF DECAY 0.36 -0.47

COEF ROOT 1.50 -0.57

H&P ERREST 0.066 -0.29

NEXT3P 0.098 -0.40

NLP 8.95 -0.66

PRIOR2P 0.44 -0.45

REFSOLN EDGE 13.87 -0.88

REFSOLN ELEM 26.29 -0.92

SMOOTH PRED 84.07 -0.89

T3S 1.01 -0.46

TYPEPARAM 19.80 -0.91

Table 3: Parameters of the least squares fit for

||ehp||E = AeBN1/3

dof for the analytic problem.

strategy factor

APRIORI 1.00

TYPEPARAM 1.23

REFSOLN ELEM 1.29

REFSOLN EDGE 1.32

SMOOTH PRED 1.72

COEF ROOT 3.01

NLP 3.06

COEF DECAY 3.79

NEXT3P 3.91

PRIOR2P 4.48

T3S 4.77

ALTERNATE 5.13

H&P ERREST 8.77

Table 4: Factor by which N is larger than the best

strategy for the analytic problem at high accuracy,

1.0x10−6.

28
Figure 32: The solution of the nearly straight reentrant corner problem.

5.2 Reentrant Corner, Nearly Straight

For elliptic partial differential equations, a reentrant (concave) corner in the domain, with interior angle ω,

causes a point singularity that behaves like r

α where r is the distance from the corner and α = π/ω. The

larger ω is, the stronger the singularity. The reentrant corner problems of the next five sections are Laplace’s

equation with Dirichlet boundary conditions on (−1, 1) × (−1, 1) with a section of angle 2π − ω removed.

The solution is

r

α

sin(αθ)

where r =

p

x

2 + y2 and θ = tan−1

(y/x).

For the nearly straight reentrant corner, ω = π + .01. If ω was π, then there would be no reentrant corner

and the solution would be linear. But with ω = π + .01 there is a very mild singularity. For this problem,

we use τ = 10−6for the grid images. The APRIORI strategy refines by h if the element contains the origin

and by p otherwise.

29
Figure 33: Example grid for the ALTERNATE strategy with the nearly straight reentrant corner problem, including details at the singularity.

Figure 34: Example grid for the APRIORI strategy

with the nearly straight reentrant corner problem,

including details at the singularity.

Figure 35: Example grid for the COEF DECAY

strategy with the nearly straight reentrant corner problem, including details at the singularity.

Figure 36: Example grid for the COEF ROOT strategy with the nearly straight reentrant corner problem, including details at the singularity.

Figure 37: Example grid for the H&P ERREST

strategy with the nearly straight reentrant corner problem, including details at the singularity.

Figure 38: Example grid for the NEXT3P strategy

with the nearly straight reentrant corner problem,

including details at the singularity.

Figure 39: Example grid for the NLP strategy with

the nearly straight reentrant corner problem, including details at the singularity.

Figure 40: Example grid for the PRIOR2P strategy

with the nearly straight reentrant corner problem,

including details at the singularity.

30
Figure 41: Example grid for the REFSOLN EDGE

strategy with the nearly straight reentrant corner problem, including details at the singularity.

Figure 42: Example grid for the REFSOLN ELEM

strategy with the nearly straight reentrant corner problem, including details at the singularity.

Figure 43: Example grid for the SMOOTH PRED

strategy with the nearly straight reentrant corner problem, including details at the singularity.

Figure 44: Example grid for the T3S strategy with

the nearly straight reentrant corner problem, including details at the singularity.

Figure 45: Example grid for the TYPEPARAM strategy with the nearly straight reentrant corner problem, including details at the singularity.

Figure 46: Log-Log plot of the convergence of the

ALTERNATE strategy with the nearly straight reentrant corner problem.

31
Figure 47: Log-Log plot of the convergence of the

APRIORI strategy with the nearly straight reentrant

corner problem.

Figure 48: Log-Log plot of the convergence of the

COEF DECAY strategy with the nearly straight

reentrant corner problem.

Figure 49: Log-Log plot of the convergence of the

COEF ROOT strategy with the nearly straight reentrant corner problem.

Figure 50: Log-Log plot of the convergence of the

H&P ERREST strategy with the nearly straight

reentrant corner problem.

32
Figure 51: Log-Log plot of the convergence of the

NEXT3P strategy with the nearly straight reentrant

corner problem.

Figure 52: Log-Log plot of the convergence of the

NLP strategy with the nearly straight reentrant corner problem.

Figure 53: Log-Log plot of the convergence of the

PRIOR2P strategy with the nearly straight reentrant

corner problem.

Figure 54: Log-Log plot of the convergence of the

REFSOLN EDGE strategy with the nearly straight

reentrant corner problem.

33
Figure 55: Log-Log plot of the convergence of the

REFSOLN ELEM strategy with the nearly straight

reentrant corner problem.

Figure 56: Log-Log plot of the convergence of the

SMOOTH PRED strategy with the nearly straight

reentrant corner problem.

Figure 57: Log-Log plot of the convergence of the

T3S strategy with the nearly straight reentrant corner problem.

Figure 58: Log-Log plot of the convergence of the

TYPEPARAM strategy with the nearly straight

reentrant corner problem.

34
Figure 59: Log-Log plot of the convergence of all strategies with the nearly straight reentrant corner problem.

35
strategy A B C

ALTERNATE 0.036 -1.39 0.25

APRIORI 3.04x10−3-0.14 0.55

COEF DECAY 0.035 -1.07 0.31

COEF ROOT 0.014 -0.64 0.37

H&P ERREST 0.056 -1.42 0.27

NEXT3P 0.29 -2.40 0.22

NLP 2.47 -3.85 0.18

PRIOR2P 0.011 -0.58 0.37

REFSOLN EDGE 0.015 -0.59 0.39

REFSOLN ELEM 4.83x10−3-0.24 0.49

SMOOTH PRED 2.15x10−3-0.13 0.52

T3S 5.64x10−3-0.45 0.36

TYPEPARAM 0.014 -0.64 0.37

Table 5: Parameters of the least squares fit for

||ehp||E = AeBNC

dof for the nearly straight reentrant

corner problem.

strategy factor

H&P ERREST 1.00

NEXT3P 1.00

COEF DECAY 1.01

NLP 1.02

COEF ROOT 1.04

REFSOLN EDGE 1.04

TYPEPARAM 1.06

PRIOR2P 1.11

REFSOLN ELEM 1.21

APRIORI 1.25

ALTERNATE 1.30

SMOOTH PRED 1.74

T3S 1.77

Table 6: Factor by which N is larger than the best

strategy for the nearly straight reentrant corner problem at low accuracy, 1.0x10−4

.

strategy A B

ALTERNATE 5.87x10−3-0.59

APRIORI 0.087 -1.04

COEF DECAY 0.019 -0.84

COEF ROOT 0.030 -0.90

H&P ERREST 0.010 -0.74

NEXT3P 8.17x10−3-0.70

NLP 5.59x10−3-0.65

PRIOR2P 0.024 -0.85

REFSOLN EDGE 0.048 -0.97

REFSOLN ELEM 0.089 -1.02

SMOOTH PRED 0.025 -0.76

T3S 9.62x10−3-0.60

TYPEPARAM 0.027 -0.88

Table 7: Parameters of the least squares fit for

||ehp||E = AeBN1/3

dof for the nearly straight reentrant

corner problem.

strategy factor

APRIORI 1.00

REFSOLN ELEM 1.05

REFSOLN EDGE 1.07

COEF ROOT 1.19

TYPEPARAM 1.27

PRIOR2P 1.36

COEF DECAY 1.36

H&P ERREST 1.65

SMOOTH PRED 1.82

NEXT3P 1.91

NLP 2.14

T3S 3.00

ALTERNATE 3.10

Table 8: Factor by which N is larger than the best

strategy for the nearly straight reentrant corner problem at high accuracy, 1.0x10−7

.

36
Figure 60: The solution of the wide angle reentrant corner problem.

5.3 Reentrant Corner, Wide Angle

This is the reentrant corner problem (Section 5.2) with ω = 5π/4. τ = 10−4for the grid images. The

APRIORI strategy refines by h if the element contains the origin and by p otherwise.

37
Figure 61: Example grid for the ALTERNATE strategy with the wide angle reentrant corner problem,

including details at the singularity.

Figure 62: Example grid for the APRIORI strategy

with the wide angle reentrant corner problem, including details at the singularity.

Figure 63: Example grid for the COEF DECAY

strategy with the wide angle reentrant corner problem, including details at the singularity.

Figure 64: Example grid for the COEF ROOT strategy with the wide angle reentrant corner problem,

including details at the singularity.

Figure 65: Example grid for the H&P ERREST

strategy with the wide angle reentrant corner problem, including details at the singularity.

Figure 66: Example grid for the NEXT3P strategy

with the wide angle reentrant corner problem, including details at the singularity.

Figure 67: Example grid for the NLP strategy with

the wide angle reentrant corner problem, including

details at the singularity.

Figure 68: Example grid for the PRIOR2P strategy

with the wide angle reentrant corner problem, including details at the singularity.

38
Figure 69: Example grid for the REFSOLN EDGE

strategy with the wide angle reentrant corner problem, including details at the singularity.

Figure 70: Example grid for the REFSOLN ELEM

strategy with the wide angle reentrant corner problem, including details at the singularity.

Figure 71: Example grid for the SMOOTH PRED

strategy with the wide angle reentrant corner problem, including details at the singularity.

Figure 72: Example grid for the T3S strategy with

the wide angle reentrant corner problem, including

details at the singularity.

Figure 73: Example grid for the TYPEPARAM strategy with the wide angle reentrant corner problem,

including details at the singularity.

Figure 74: Log-Log plot of the convergence of the

ALTERNATE strategy with the wide angle reentrant

corner problem.

39
Figure 75: Log-Log plot of the convergence of the

APRIORI strategy with the wide angle reentrant corner problem.

Figure 76: Log-Log plot of the convergence of the

COEF DECAY strategy with the wide angle reentrant corner problem.

Figure 77: Log-Log plot of the convergence of the

COEF ROOT strategy with the wide angle reentrant

corner problem.

Figure 78: Log-Log plot of the convergence of the

H&P ERREST strategy with the wide angle reentrant corner problem.

40
Figure 79: Log-Log plot of the convergence of the

NEXT3P strategy with the wide angle reentrant corner problem.

Figure 80: Log-Log plot of the convergence of the

NLP strategy with the wide angle reentrant corner problem.

Figure 81: Log-Log plot of the convergence of the

PRIOR2P strategy with the wide angle reentrant corner problem.

Figure 82: Log-Log plot of the convergence of the

REFSOLN EDGE strategy with the wide angle reentrant corner problem.

41
Figure 83: Log-Log plot of the convergence of the

REFSOLN ELEM strategy with the wide angle reentrant corner problem.

Figure 84: Log-Log plot of the convergence of the

SMOOTH PRED strategy with the wide angle reentrant corner problem.

Figure 85: Log-Log plot of the convergence of the T3S

strategy with the wide angle reentrant corner problem.

Figure 86: Log-Log plot of the convergence of the

TYPEPARAM strategy with the wide angle reentrant corner problem.

42
Figure 87: Log-Log plot of the convergence of all strategies with the wide angle reentrant corner problem.

43
strategy A B C

ALTERNATE 1.47 -1.22 0.24

APRIORI 0.49 -0.30 0.44

COEF DECAY 6.35 -1.59 0.25

COEF ROOT 2.08 -1.03 0.29

H&P ERREST 5.29 -1.62 0.24

NEXT3P 2.09 -1.16 0.27

NLP 0.19 -0.35 0.37

PRIOR2P 0.47 -0.42 0.38

REFSOLN EDGE 0.42 -0.34 0.42

REFSOLN ELEM 0.43 -0.29 0.44

SMOOTH PRED 0.23 -0.18 0.47

T3S 2.56 -1.40 0.22

TYPEPARAM 0.45 -0.48 0.36

Table 9: Parameters of the least squares fit for

||ehp||E = AeBNC

dof for the wide angle reentrant corner problem.

strategy factor

COEF DECAY 1.00

COEF ROOT 1.05

H&P ERREST 1.07

REFSOLN EDGE 1.10

NEXT3P 1.14

PRIOR2P 1.16

NLP 1.18

REFSOLN ELEM 1.20

APRIORI 1.24

TYPEPARAM 1.27

ALTERNATE 1.35

SMOOTH PRED 1.66

T3S 1.88

Table 10: Factor by which N is larger than the best

strategy for the wide angle reentrant corner problem

at low accuracy, 1.0x10−2.

strategy A B

ALTERNATE 0.13 -0.39

APRIORI 6.37 -0.92

COEF DECAY 0.40 -0.61

COEF ROOT 0.63 -0.65

H&P ERREST 0.27 -0.54

NEXT3P 0.37 -0.55

NLP 0.46 -0.54

PRIOR2P 1.53 -0.73

REFSOLN EDGE 3.97 -0.87

REFSOLN ELEM 7.74 -0.92

SMOOTH PRED 3.38 -0.75

T3S 0.11 -0.34

TYPEPARAM 0.78 -0.62

Table 11: Parameters of the least squares fit for

||ehp||E = AeBN1/3

dof for the wide angle reentrant corner problem.

strategy factor

APRIORI 1.00

REFSOLN ELEM 1.02

REFSOLN EDGE 1.07

PRIOR2P 1.46

SMOOTH PRED 1.62

COEF ROOT 1.71

COEF DECAY 1.79

TYPEPARAM 2.06

H&P ERREST 2.43

NEXT3P 2.52

NLP 2.70

ALTERNATE 5.49

T3S 8.11

Table 12: Factor by which N is larger than the best

strategy for the wide angle reentrant corner problem

at high accuracy, 1.0x10−6.

44
Figure 88: The solution of the L-shaped domain problem.

5.4 Reentrant Corner, L-Shaped Domain

The reentrant corner problem (Section 5.2) with ω = 3π/2 is the classic “L domain” problem which is used

as an example in many papers on adaptive grid refinement. τ = 10−4for the grid images. The APRIORI

strategy refines by h if the element contains the origin and by p otherwise. For this problem, the cube root

vs. log convergence plots are shown in addition to the log-log plots.

45
Figure 89: Example grid for the ALTERNATE strategy with the L-shaped domain problem, including details at the singularity.

Figure 90: Example grid for the APRIORI strategy

with the L-shaped domain problem, including details

at the singularity.

Figure 91: Example grid for the COEF DECAY

strategy with the L-shaped domain problem, including details at the singularity.

Figure 92: Example grid for the COEF ROOT strategy with the L-shaped domain problem, including details at the singularity.

Figure 93: Example grid for the H&P ERREST

strategy with the L-shaped domain problem, including details at the singularity.

Figure 94: Example grid for the NEXT3P strategy

with the L-shaped domain problem, including details

at the singularity.

Figure 95: Example grid for the NLP strategy with

the L-shaped domain problem, including details at

the singularity.

Figure 96: Example grid for the PRIOR2P strategy

with the L-shaped domain problem, including details

at the singularity.

46
Figure 97: Example grid for the REFSOLN EDGE

strategy with the L-shaped domain problem, including details at the singularity.

Figure 98: Example grid for the REFSOLN ELEM

strategy with the L-shaped domain problem, including details at the singularity.

Figure 99: Example grid for the SMOOTH PRED

strategy with the L-shaped domain problem, including details at the singularity.

Figure 100: Example grid for the T3S strategy with

the L-shaped domain problem, including details at

the singularity.

Figure 101: Example grid for the TYPEPARAM

strategy with the L-shaped domain problem, including details at the singularity.

Figure 102: Log-Log plot of the convergence of

the ALTERNATE strategy with the L-shaped domain problem.

47
Figure 103: Log-Log plot of the convergence of the

APRIORI strategy with the L-shaped domain problem.

Figure 104: Log-Log plot of the convergence of

the COEF DECAY strategy with the L-shaped domain problem.

Figure 105: Log-Log plot of the convergence of

the COEF ROOT strategy with the L-shaped domain problem.

Figure 106: Log-Log plot of the convergence of

the H&P ERREST strategy with the L-shaped domain problem.

48
Figure 107: Log-Log plot of the convergence of the

NEXT3P strategy with the L-shaped domain problem.

Figure 108: Log-Log plot of the convergence of the

NLP strategy with the L-shaped domain problem.

Figure 109: Log-Log plot of the convergence of the

PRIOR2P strategy with the L-shaped domain problem.

Figure 110: Log-Log plot of the convergence of the

REFSOLN EDGE strategy with the L-shaped domain problem.

49
Figure 111: Log-Log plot of the convergence of the

REFSOLN ELEM strategy with the L-shaped domain problem.

Figure 112: Log-Log plot of the convergence of the

SMOOTH PRED strategy with the L-shaped domain problem.

Figure 113: Log-Log plot of the convergence of the

T3S strategy with the L-shaped domain problem.

Figure 114: Log-Log plot of the convergence of

the TYPEPARAM strategy with the L-shaped domain problem.

50
Figure 115: Log-Log plot of the convergence of all strategies with the L-shaped domain problem.

51
Figure 116: Cube root vs. Log plot of the convergence of the ALTERNATE strategy with the Lshaped domain problem.

Figure 117: Cube root vs. Log plot of the convergence of the APRIORI strategy with the L-shaped

domain problem.

Figure 118: Cube root vs. Log plot of the convergence of the COEF DECAY strategy with the Lshaped domain problem.

Figure 119: Cube root vs. Log plot of the convergence of the COEF ROOT strategy with the Lshaped domain problem.

52
Figure 120: Cube root vs. Log plot of the convergence of the H&P ERREST strategy with the Lshaped domain problem.

Figure 121: Cube root vs. Log plot of the convergence of the NEXT3P strategy with the L-shaped

domain problem.

Figure 122: Cube root vs. Log plot of the convergence of the NLP strategy with the L-shaped domain problem.

Figure 123: Cube root vs. Log plot of the convergence of the PRIOR2P strategy with the L-shaped

domain problem.

53
Figure 124: Cube root vs. Log plot of the convergence of the REFSOLN EDGE strategy with the Lshaped domain problem.

Figure 125: Cube root vs. Log plot of the convergence of the REFSOLN ELEM strategy with the Lshaped domain problem.

Figure 126: Cube root vs. Log plot of the convergence of the SMOOTH PRED strategy with the Lshaped domain problem.

Figure 127: Cube root vs. Log plot of the convergence of the T3S strategy with the L-shaped domain problem.

54
Figure 128: Cube root vs. Log plot of the convergence of the TYPEPARAM strategy with the Lshaped domain problem.

55
Figure 129: Cube root vs. Log plot of the convergence of all strategies with the L-shaped domain problem.

56
strategy A B C

ALTERNATE 2.86 -1.15 0.24

APRIORI 1.30 -0.35 0.41

COEF DECAY 20.31 -1.85 0.23

COEF ROOT 3.32 -0.95 0.28

H&P ERREST 1.74 -0.74 0.30

NEXT3P 3.40 -1.14 0.25

NLP 0.094 -0.14 0.44

PRIOR2P 0.84 -0.40 0.37

REFSOLN EDGE 0.81 -0.34 0.41

REFSOLN ELEM 0.89 -0.37 0.38

SMOOTH PRED 0.43 -0.17 0.45

T3S 2.76 -1.10 0.23

TYPEPARAM 0.72 -0.40 0.36

Table 13: Parameters of the least squares fit for

||ehp||E = AeBNC

dof for the L-shaped domain problem.

strategy factor

COEF DECAY 1.00

REFSOLN EDGE 1.01

COEF ROOT 1.13

NLP 1.14

APRIORI 1.18

PRIOR2P 1.24

H&P ERREST 1.27

NEXT3P 1.32

REFSOLN ELEM 1.32

TYPEPARAM 1.39

ALTERNATE 1.77

SMOOTH PRED 1.77

T3S 2.54

Table 14: Factor by which N is larger than the best

strategy for the L-shaped domain problem at low accuracy, 1.0x10−2

.

strategy A B

ALTERNATE 0.23 -0.33

APRIORI 9.70 -0.81

COEF DECAY 0.44 -0.50

COEF ROOT 0.81 -0.54

H&P ERREST 0.79 -0.51

NEXT3P 0.39 -0.42

NLP 0.70 -0.46

PRIOR2P 2.21 -0.63

REFSOLN EDGE 5.81 -0.79

REFSOLN ELEM 3.28 -0.66

SMOOTH PRED 4.99 -0.64

T3S 0.19 -0.28

TYPEPARAM 1.38 -0.55

Table 15: Parameters of the least squares fit for

||ehp||E = AeBN1/3

dof for the L-shaped domain problem.

strategy factor

APRIORI 1.00

REFSOLN EDGE 1.00

REFSOLN ELEM 1.54

PRIOR2P 1.61

SMOOTH PRED 1.77

COEF ROOT 2.03

COEF DECAY 2.08

TYPEPARAM 2.09

H&P ERREST 2.48

NLP 3.03

NEXT3P 3.67

ALTERNATE 6.90

T3S 11.55

Table 16: Factor by which N is larger than the best

strategy for the L-shaped domain problem at high

accuracy, 1.0x10−6.

57
Figure 130: The solution of the narrow angle reentrant corner problem.

5.5 Reentrant Corner, Narrow Angle

This is the reentrant corner problem (Section 5.2) with ω = 7π/4. τ = 10−4for the grid images. The

APRIORI strategy refines by h if the element contains the origin and by p otherwise.

58
Figure 131: Example grid for the ALTERNATE

strategy with the narrow angle reentrant corner problem, including details at the singularity.

Figure 132: Example grid for the APRIORI strategy with the narrow angle reentrant corner problem,

including details at the singularity.

Figure 133: Example grid for the COEF DECAY

strategy with the narrow angle reentrant corner problem, including details at the singularity.

Figure 134: Example grid for the COEF ROOT

strategy with the narrow angle reentrant corner problem, including details at the singularity.

Figure 135: Example grid for the H&P ERREST

strategy with the narrow angle reentrant corner problem, including details at the singularity.

Figure 136: Example grid for the NEXT3P strategy

with the narrow angle reentrant corner problem, including details at the singularity.

Figure 137: Example grid for the NLP strategy with

the narrow angle reentrant corner problem, including

details at the singularity.

Figure 138: Example grid for the PRIOR2P strategy with the narrow angle reentrant corner problem,

including details at the singularity.

59
Figure 139: Example grid for the REFSOLN EDGE

strategy with the narrow angle reentrant corner problem, including details at the singularity.

Figure 140: Example grid for the REFSOLN ELEM

strategy with the narrow angle reentrant corner problem, including details at the singularity.

Figure 141: Example grid for the SMOOTH PRED

strategy with the narrow angle reentrant corner problem, including details at the singularity.

Figure 142: Example grid for the T3S strategy with

the narrow angle reentrant corner problem, including

details at the singularity.

Figure 143: Example grid for the TYPEPARAM

strategy with the narrow angle reentrant corner problem, including details at the singularity.

Figure 144: Log-Log plot of the convergence of the

ALTERNATE strategy with the narrow angle reentrant corner problem.

60
Figure 145: Log-Log plot of the convergence of the

APRIORI strategy with the narrow angle reentrant

corner problem.

Figure 146: Log-Log plot of the convergence of the

COEF DECAY strategy with the narrow angle reentrant corner problem.

Figure 147: Log-Log plot of the convergence of the

COEF ROOT strategy with the narrow angle reentrant corner problem.

Figure 148: Log-Log plot of the convergence of the

H&P ERREST strategy with the narrow angle reentrant corner problem.

61
Figure 149: Log-Log plot of the convergence of the

NEXT3P strategy with the narrow angle reentrant

corner problem.

Figure 150: Log-Log plot of the convergence of the

NLP strategy with the narrow angle reentrant corner problem.

Figure 151: Log-Log plot of the convergence of the

PRIOR2P strategy with the narrow angle reentrant

corner problem.

Figure 152: Log-Log plot of the convergence of the

REFSOLN EDGE strategy with the narrow angle

reentrant corner problem.

62
Figure 153: Log-Log plot of the convergence of the

REFSOLN ELEM strategy with the narrow angle

reentrant corner problem.

Figure 154: Log-Log plot of the convergence of the

SMOOTH PRED strategy with the narrow angle

reentrant corner problem.

Figure 155: Log-Log plot of the convergence of the

T3S strategy with the narrow angle reentrant corner problem.

Figure 156: Log-Log plot of the convergence of the

TYPEPARAM strategy with the narrow angle reentrant corner problem.

63
Figure 157: Log-Log plot of the convergence of all strategies with the narrow angle reentrant corner problem.

64
strategy A B C

ALTERNATE 2.31 -0.83 0.25

APRIORI 1.75 -0.33 0.41

COEF DECAY 36.40 -1.90 0.22

COEF ROOT 6.61 -1.05 0.27

H&P ERREST 1.28 -0.47 0.33

NEXT3P 2.72 -0.83 0.27

NLP 14.36 -0.99 0.27

PRIOR2P 1.55 -0.45 0.35

REFSOLN EDGE 0.92 -0.29 0.42

REFSOLN ELEM 0.53 -0.13 0.49

SMOOTH PRED 0.45 -0.13 0.47

T3S 0.25 -0.24 0.33

TYPEPARAM 1.39 -0.46 0.34

Table 17: Parameters of the least squares fit for

||ehp||E = AeBNC

dof for the narrow angle reentrant

corner problem.

strategy factor

REFSOLN EDGE 1.00

COEF DECAY 1.06

APRIORI 1.18

COEF ROOT 1.19

REFSOLN ELEM 1.28

PRIOR2P 1.29

TYPEPARAM 1.51

H&P ERREST 1.54

NEXT3P 1.57

SMOOTH PRED 1.78

NLP 1.95

ALTERNATE 2.14

T3S 3.66

Table 18: Factor by which N is larger than the best

strategy for the narrow angle reentrant corner problem at low accuracy, 1.0x10−2

.

strategy A B

ALTERNATE 0.35 -0.30

APRIORI 12.03 -0.73

COEF DECAY 0.49 -0.44

COEF ROOT 0.87 -0.47

H&P ERREST 1.17 -0.45

NEXT3P 0.59 -0.38

NLP 2.26 -0.48

PRIOR2P 2.36 -0.55

REFSOLN EDGE 6.93 -0.71

REFSOLN ELEM 11.62 -0.72

SMOOTH PRED 7.64 -0.60

T3S 0.23 -0.22

TYPEPARAM 1.51 -0.48

Table 19: Parameters of the least squares fit for

||ehp||E = AeBN1/3

dof for the narrow angle reentrant

corner problem.

strategy factor

REFSOLN EDGE 1.00

REFSOLN ELEM 1.00

APRIORI 1.01

SMOOTH PRED 1.69

PRIOR2P 1.74

COEF ROOT 2.25

COEF DECAY 2.28

TYPEPARAM 2.38

NLP 2.68

H&P ERREST 2.69

NEXT3P 3.97

ALTERNATE 7.30

T3S 15.52

Table 20: Factor by which N is larger than the best

strategy for the narrow angle reentrant corner problem at high accuracy, 1.0x10−6

.

65
Figure 158: The solution of the slit domain problem.

5.6 Reentrant Corner, Slit

This is the reentrant corner problem (Section 5.2) with ω = 2π. This results in a domain that has a slit

along the positive x axis. τ = 10−4for the grid images. The APRIORI strategy refines by h if the element

contains the origin and by p otherwise.

66
Figure 159: Example grid for the ALTERNATE

strategy with the slit domain problem, including details at the singularity.

Figure 160: Example grid for the APRIORI strategy

with the slit domain problem, including details at the

singularity.

Figure 161: Example grid for the COEF DECAY

strategy with the slit domain problem, including details at the singularity.

Figure 162: Example grid for the COEF ROOT

strategy with the slit domain problem, including details at the singularity.

Figure 163: Example grid for the H&P ERREST

strategy with the slit domain problem, including details at the singularity.

Figure 164: Example grid for the NEXT3P strategy

with the slit domain problem, including details at the

singularity.

Figure 165: Example grid for the NLP strategy with

the slit domain problem, including details at the singularity.

Figure 166: Example grid for the PRIOR2P strategy

with the slit domain problem, including details at the

singularity.

67
Figure 167: Example grid for the REFSOLN EDGE

strategy with the slit domain problem, including details at the singularity.

Figure 168: Example grid for the REFSOLN ELEM

strategy with the slit domain problem, including details at the singularity.

Figure 169: Example grid for the SMOOTH PRED

strategy with the slit domain problem, including details at the singularity.

Figure 170: Example grid for the T3S strategy with

the slit domain problem, including details at the singularity.

Figure 171: Example grid for the TYPEPARAM

strategy with the slit domain problem, including details at the singularity.

Figure 172: Log-Log plot of the convergence of the

ALTERNATE strategy with the slit domain problem.

68
Figure 173: Log-Log plot of the convergence of the

APRIORI strategy with the slit domain problem.

Figure 174: Log-Log plot of the convergence of the

COEF DECAY strategy with the slit domain problem.

Figure 175: Log-Log plot of the convergence of the

COEF ROOT strategy with the slit domain problem.

Figure 176: Log-Log plot of the convergence of the

H&P ERREST strategy with the slit domain problem.

69
Figure 177: Log-Log plot of the convergence of the

NEXT3P strategy with the slit domain problem.

Figure 178: Log-Log plot of the convergence of the

NLP strategy with the slit domain problem.

Figure 179: Log-Log plot of the convergence of the

PRIOR2P strategy with the slit domain problem.

Figure 180: Log-Log plot of the convergence of

the REFSOLN EDGE strategy with the slit domain problem.

70
Figure 181: Log-Log plot of the convergence of

the REFSOLN ELEM strategy with the slit domain problem.

Figure 182: Log-Log plot of the convergence of the

SMOOTH PRED strategy with the slit domain problem.

Figure 183: Log-Log plot of the convergence of the

T3S strategy with the slit domain problem.

Figure 184: Log-Log plot of the convergence of the

TYPEPARAM strategy with the slit domain problem.

71
Figure 185: Log-Log plot of the convergence of all strategies with the slit domain problem.

72
strategy A B C

ALTERNATE 1.41 -0.49 0.29

APRIORI 1.89 -0.30 0.40

COEF DECAY 44.70 -1.81 0.22

COEF ROOT 10.14 -1.08 0.26

H&P ERREST 1.62 -0.43 0.33

NEXT3P 1.10 -0.31 0.36

NLP 0.11 -0.038 0.53

PRIOR2P 1.74 -0.39 0.35

REFSOLN EDGE 1.17 -0.29 0.40

REFSOLN ELEM 2.17 -0.38 0.36

SMOOTH PRED 0.70 -0.14 0.45

T3S 0.17 -0.086 0.40

TYPEPARAM 6.24 -0.78 0.30

Table 21: Parameters of the least squares fit for

||ehp||E = AeBNC

dof for the slit domain problem.

strategy factor

REFSOLN EDGE 1.00

COEF DECAY 1.18

APRIORI 1.18

TYPEPARAM 1.21

COEF ROOT 1.30

REFSOLN ELEM 1.48

PRIOR2P 1.48

H&P ERREST 1.74

NEXT3P 1.86

SMOOTH PRED 1.86

NLP 2.41

ALTERNATE 2.99

T3S 6.11

Table 22: Factor by which N is larger than the best

strategy for the slit domain problem at low accuracy,

1.0x10−2.

strategy A B

ALTERNATE 0.54 -0.27

APRIORI 12.72 -0.67

COEF DECAY 0.57 -0.39

COEF ROOT 0.97 -0.42

H&P ERREST 1.54 -0.41

NEXT3P 1.74 -0.42

NLP 3.08 -0.41

PRIOR2P 2.92 -0.49

REFSOLN EDGE 7.35 -0.65

REFSOLN ELEM 4.92 -0.54

SMOOTH PRED 9.52 -0.55

T3S 0.40 -0.21

TYPEPARAM 1.96 -0.49

Table 23: Parameters of the least squares fit for

||ehp||E = AeBN1/3

dof for the slit domain problem.

strategy factor

REFSOLN EDGE 1.00

APRIORI 1.01

REFSOLN ELEM 1.60

SMOOTH PRED 1.65

TYPEPARAM 1.70

PRIOR2P 1.86

COEF ROOT 2.37

COEF DECAY 2.48

NEXT3P 2.66

H&P ERREST 2.74

NLP 3.18

ALTERNATE 8.05

T3S 15.97

Table 24: Factor by which N is larger than the best

strategy for the slit domain problem at high accuracy,

1.0x10−6.

73
Figure 186: The u component of the solution of the mode 1 linear elasticity problem.

Figure 187: The v component of the solution of the mode 1 linear elasticity problem.

5.7 Linear Elasticity, Mode 1

The linear elasticity problem is a coupled system of two equations with a mixed derivative in the coupling

term and different coefficients on the second order x and y terms. The domain is a square with a slit, as in

the reentrant corner slit domain problem (Section 5.6). The boundary conditions are Dirichlet. For further

details, see [21]. We consider two solutions, refered to as mode 1 and mode 2, by using different boundary

conditions. Both solutions have a singularity at the origin, with the mode 1 solution having the stronger

singularity. This section contains the results for the mode 1 solution. τ = 10−3for the grid images. The

APRIORI strategy refines by h if the element contains the origin and by p otherwise.

74
Figure 188: Example grid for the ALTERNATE

strategy with the mode 1 linear elasticity problem,

including details at the singularity.

Figure 189: Example grid for the APRIORI strategy

with the mode 1 linear elasticity problem, including

details at the singularity.

Figure 190: Example grid for the COEF DECAY

strategy with the mode 1 linear elasticity problem,

including details at the singularity.

Figure 191: Example grid for the COEF ROOT

strategy with the mode 1 linear elasticity problem,

including details at the singularity.

Figure 192: Example grid for the H&P ERREST

strategy with the mode 1 linear elasticity problem,

including details at the singularity.

Figure 193: Example grid for the NEXT3P strategy

with the mode 1 linear elasticity problem, including

details at the singularity.

Figure 194: Example grid for the NLP strategy with

the mode 1 linear elasticity problem, including details

at the singularity.

Figure 195: Example grid for the PRIOR2P strategy

with the mode 1 linear elasticity problem, including

details at the singularity.

75
Figure 196: Example grid for the REFSOLN EDGE

strategy with the mode 1 linear elasticity problem,

including details at the singularity.

Figure 197: Example grid for the REFSOLN ELEM

strategy with the mode 1 linear elasticity problem,

including details at the singularity.

Figure 198: Example grid for the SMOOTH PRED

strategy with the mode 1 linear elasticity problem,

including details at the singularity.

Figure 199: Example grid for the T3S strategy with

the mode 1 linear elasticity problem, including details

at the singularity.

Figure 200: Example grid for the TYPEPARAM

strategy with the mode 1 linear elasticity problem,

including details at the singularity.

Figure 201: Log-Log plot of the convergence of the

ALTERNATE strategy with the mode 1 linear elasticity problem.

76
Figure 202: Log-Log plot of the convergence of the

APRIORI strategy with the mode 1 linear elasticity problem.

Figure 203: Log-Log plot of the convergence of the

COEF DECAY strategy with the mode 1 linear elasticity problem.

Figure 204: Log-Log plot of the convergence of the

COEF ROOT strategy with the mode 1 linear elasticity problem.

Figure 205: Log-Log plot of the convergence of the

H&P ERREST strategy with the mode 1 linear elasticity problem.

77
Figure 206: Log-Log plot of the convergence of the

NEXT3P strategy with the mode 1 linear elasticity problem.

Figure 207: Log-Log plot of the convergence of the

NLP strategy with the mode 1 linear elasticity problem.

Figure 208: Log-Log plot of the convergence of the

PRIOR2P strategy with the mode 1 linear elasticity problem.

Figure 209: Log-Log plot of the convergence of the

REFSOLN EDGE strategy with the mode 1 linear

elasticity problem.

78
Figure 210: Log-Log plot of the convergence of the

REFSOLN ELEM strategy with the mode 1 linear

elasticity problem.

Figure 211: Log-Log plot of the convergence of the

SMOOTH PRED strategy with the mode 1 linear

elasticity problem.

Figure 212: Log-Log plot of the convergence of the

T3S strategy with the mode 1 linear elasticity problem.

Figure 213: Log-Log plot of the convergence of the

TYPEPARAM strategy with the mode 1 linear elasticity problem.

79
Figure 214: Log-Log plot of the convergence of all strategies with the mode 1 linear elasticity problem.

80
strategy A B C

ALTERNATE 2.92 -0.39 0.29

APRIORI 5.11 -0.28 0.38

COEF DECAY 20.25 -1.06 0.24

COEF ROOT 4.27 -0.53 0.29

H&P ERREST 1.97 -0.31 0.33

NEXT3P 9.44x1016 -33.00 0.033

NLP 0.44 -0.068 0.45

PRIOR2P 1.51 -0.26 0.34

REFSOLN EDGE 2.30 -0.23 0.40

REFSOLN ELEM 2.42 -0.19 0.40

SMOOTH PRED 0.94 -0.088 0.45

T3S 0.33 -0.066 0.41

TYPEPARAM 2.91 -0.33 0.33

Table 25: Parameters of the least squares fit for

||ehp||E = AeBNC

dof for the mode 1 linear elasticity problem.

strategy factor

REFSOLN EDGE 1.00

APRIORI 1.17

COEF DECAY 1.39

REFSOLN ELEM 1.56

COEF ROOT 1.63

NEXT3P 1.69

TYPEPARAM 1.70

H&P ERREST 1.77

PRIOR2P 1.90

SMOOTH PRED 2.06

NLP 2.29

ALTERNATE 3.43

T3S 6.06

Table 26: Factor by which N is larger than the best

strategy for the mode 1 linear elasticity problem at

low accuracy, 1.0x10−2.

strategy A B

ALTERNATE 0.96 -0.21

APRIORI 20.92 -0.50

COEF DECAY 0.71 -0.27

COEF ROOT 1.16 -0.28

H&P ERREST 1.90 -0.30

NEXT3P 0.017 -0.078

NLP 4.74 -0.32

PRIOR2P 1.81 -0.29

REFSOLN EDGE 11.91 -0.49

REFSOLN ELEM 13.58 -0.43

SMOOTH PRED 12.51 -0.39

T3S 1.14 -0.18

TYPEPARAM 2.99 -0.33

Table 27: Parameters of the least squares fit for

||ehp||E = AeBN1/3

dof for the mode 1 linear elasticity problem.

strategy factor

REFSOLN EDGE 1.00

APRIORI 1.04

REFSOLN ELEM 1.55

SMOOTH PRED 1.97

TYPEPARAM 2.51

NLP 2.85

H&P ERREST 3.06

COEF DECAY 3.24

PRIOR2P 3.33

COEF ROOT 3.36

ALTERNATE 7.90

T3S 11.93

NEXT3P 46.52

Table 28: Factor by which N is larger than the best

strategy for the mode 1 linear elasticity problem at

high accuracy, 1.0x10−6.

81
Figure 215: The u component of the solution of the mode 2 linear elasticity problem.

Figure 216: The v component of the solution of the mode 2 linear elasticity problem.

5.8 Linear Elasticity, Mode 2

This is the mode 2 solution of the linear elasticity problem (Section 5.7). τ = 10−3for the grid images. The

APRIORI strategy refines by h if the element contains the origin and by p otherwise.

82
Figure 217: Example grid for the ALTERNATE

strategy with the mode 2 linear elasticity problem,

including details at the singularity.

Figure 218: Example grid for the APRIORI strategy

with the mode 2 linear elasticity problem, including

details at the singularity.

Figure 219: Example grid for the COEF DECAY

strategy with the mode 2 linear elasticity problem,

including details at the singularity.

Figure 220: Example grid for the COEF ROOT

strategy with the mode 2 linear elasticity problem,

including details at the singularity.

Figure 221: Example grid for the H&P ERREST

strategy with the mode 2 linear elasticity problem,

including details at the singularity.

Figure 222: Example grid for the NEXT3P strategy

with the mode 2 linear elasticity problem, including

details at the singularity.

Figure 223: Example grid for the NLP strategy with

the mode 2 linear elasticity problem, including details

at the singularity.

Figure 224: Example grid for the PRIOR2P strategy

with the mode 2 linear elasticity problem, including

details at the singularity.

83
Figure 225: Example grid for the REFSOLN EDGE

strategy with the mode 2 linear elasticity problem,

including details at the singularity.

Figure 226: Example grid for the REFSOLN ELEM

strategy with the mode 2 linear elasticity problem,

including details at the singularity.

Figure 227: Example grid for the SMOOTH PRED

strategy with the mode 2 linear elasticity problem,

including details at the singularity.

Figure 228: Example grid for the T3S strategy with

the mode 2 linear elasticity problem, including details

at the singularity.

Figure 229: Example grid for the TYPEPARAM

strategy with the mode 2 linear elasticity problem,

including details at the singularity.

Figure 230: Log-Log plot of the convergence of the

ALTERNATE strategy with the mode 2 linear elasticity problem.

84
Figure 231: Log-Log plot of the convergence of the

APRIORI strategy with the mode 2 linear elasticity problem.

Figure 232: Log-Log plot of the convergence of the

COEF DECAY strategy with the mode 2 linear elasticity problem.

Figure 233: Log-Log plot of the convergence of the

COEF ROOT strategy with the mode 2 linear elasticity problem.

Figure 234: Log-Log plot of the convergence of the

H&P ERREST strategy with the mode 2 linear elasticity problem.

85
Figure 235: Log-Log plot of the convergence of the

NEXT3P strategy with the mode 2 linear elasticity problem.

Figure 236: Log-Log plot of the convergence of the

NLP strategy with the mode 2 linear elasticity problem.

Figure 237: Log-Log plot of the convergence of the

PRIOR2P strategy with the mode 2 linear elasticity problem.

Figure 238: Log-Log plot of the convergence of the

REFSOLN EDGE strategy with the mode 2 linear

elasticity problem.

86
Figure 239: Log-Log plot of the convergence of the

REFSOLN ELEM strategy with the mode 2 linear

elasticity problem.

Figure 240: Log-Log plot of the convergence of the

SMOOTH PRED strategy with the mode 2 linear

elasticity problem.

Figure 241: Log-Log plot of the convergence of the

T3S strategy with the mode 2 linear elasticity problem.

Figure 242: Log-Log plot of the convergence of the

TYPEPARAM strategy with the mode 2 linear elasticity problem.

87
Figure 243: Log-Log plot of the convergence of all strategies with the mode 2 linear elasticity problem.

88
strategy A B C

ALTERNATE 1.63 -0.88 0.24

APRIORI 0.38 -0.15 0.46

COEF DECAY 3.27 -0.96 0.26

COEF ROOT 1.95 -0.74 0.28

H&P ERREST 6.51 -1.29 0.23

NEXT3P 8.60 -1.86 0.18

NLP 0.70 -0.34 0.35

PRIOR2P 0.66 -0.38 0.34

REFSOLN EDGE 0.88 -0.32 0.38

REFSOLN ELEM 0.54 -0.21 0.42

SMOOTH PRED 0.14 -0.063 0.50

T3S 0.69 -0.49 0.29

TYPEPARAM 271.46 -3.90 0.14

Table 29: Parameters of the least squares fit for

||ehp||E = AeBNC

dof for the mode 2 linear elasticity problem.

strategy factor

REFSOLN EDGE 1.00

TYPEPARAM 1.03

COEF DECAY 1.03

COEF ROOT 1.06

H&P ERREST 1.10

PRIOR2P 1.16

REFSOLN ELEM 1.18

APRIORI 1.19

NLP 1.34

NEXT3P 1.35

ALTERNATE 1.48

SMOOTH PRED 1.87

T3S 1.88

Table 30: Factor by which N is larger than the best

strategy for the mode 2 linear elasticity problem at

low accuracy, 1.0x10−2.

strategy A B

ALTERNATE 0.12 -0.25

APRIORI 5.72 -0.59

COEF DECAY 0.37 -0.38

COEF ROOT 0.49 -0.40

H&P ERREST 0.22 -0.33

NEXT3P 0.11 -0.23

NLP 1.05 -0.43

PRIOR2P 0.86 -0.43

REFSOLN EDGE 3.12 -0.58

REFSOLN ELEM 4.15 -0.56

SMOOTH PRED 2.59 -0.45

T3S 0.21 -0.26

TYPEPARAM 0.070 -0.24

Table 31: Parameters of the least squares fit for

||ehp||E = AeBN1/3

dof for the mode 2 linear elasticity problem.

strategy factor

REFSOLN EDGE 1.00

APRIORI 1.03

REFSOLN ELEM 1.14

PRIOR2P 1.84

NLP 1.96

COEF ROOT 2.01

SMOOTH PRED 2.04

COEF DECAY 2.15

H&P ERREST 2.75

TYPEPARAM 5.66

T3S 5.74

ALTERNATE 5.81

NEXT3P 8.76

Table 32: Factor by which N is larger than the best

strategy for the mode 2 linear elasticity problem at

high accuracy, 1.0x10−6.

89
Figure 244: The solution of the mild peak problem.

5.9 Mild Peak

The peak problem contains a Gaussian peak in the interior of the domain. It is Poisson’s equation on the

unit square with Dirichlet boundary conditions. The solution is

e

−α((x−xc)

2+(y−yc)2

)

where (xc, yc) is the location of the peak, and α determines the strength of the peak. For the easy form

of this problem, we use α = 1000 and (xc, yc) = (0.5, 0.5). For this problem, we used τ = 10−5for the

grid images. The APRIORI strategy refines by h if the element touches the center of the peak and by p

otherwise.

90
Figure 245: Example grid for the ALTERNATE

strategy with the mild peak problem.

Figure 246: Example grid for the APRIORI strategy

with the mild peak problem.

Figure 247: Example grid for the COEF DECAY

strategy with the mild peak problem.

Figure 248: Example grid for the COEF ROOT

strategy with the mild peak problem.

Figure 249: Example grid for the H&P ERREST

strategy with the mild peak problem.

Figure 250: Example grid for the NEXT3P strategy

with the mild peak problem.

91
Figure 251: Example grid for the NLP strategy with

the mild peak problem.

Figure 252: Example grid for the PRIOR2P strategy

with the mild peak problem.

Figure 253: Example grid for the REFSOLN EDGE

strategy with the mild peak problem.

Figure 254: Example grid for the REFSOLN ELEM

strategy with the mild peak problem.

Figure 255: Example grid for the SMOOTH PRED

strategy with the mild peak problem.

Figure 256: Example grid for the T3S strategy with

the mild peak problem.

92
Figure 257: Example grid for the TYPEPARAM

strategy with the mild peak problem.

Figure 258: Log-Log plot of the convergence of the

ALTERNATE strategy with the mild peak problem.

Figure 259: Log-Log plot of the convergence of the

APRIORI strategy with the mild peak problem.

Figure 260: Log-Log plot of the convergence of the

COEF DECAY strategy with the mild peak problem.

93
Figure 261: Log-Log plot of the convergence of the

COEF ROOT strategy with the mild peak problem.

Figure 262: Log-Log plot of the convergence of the

H&P ERREST strategy with the mild peak problem.

Figure 263: Log-Log plot of the convergence of the

NEXT3P strategy with the mild peak problem.

Figure 264: Log-Log plot of the convergence of the

NLP strategy with the mild peak problem.

94
Figure 265: Log-Log plot of the convergence of the

PRIOR2P strategy with the mild peak problem.

Figure 266: Log-Log plot of the convergence of the

REFSOLN EDGE strategy with the mild peak problem.

Figure 267: Log-Log plot of the convergence of the

REFSOLN ELEM strategy with the mild peak problem.

Figure 268: Log-Log plot of the convergence of the

SMOOTH PRED strategy with the mild peak problem.

95
Figure 269: Log-Log plot of the convergence of the

T3S strategy with the mild peak problem.

Figure 270: Log-Log plot of the convergence of the

TYPEPARAM strategy with the mild peak problem.

96
Figure 271: Log-Log plot of the convergence of all strategies with the mild peak problem.

97
strategy A B C

ALTERNATE 1.06 -0.31 0.36

APRIORI 6.34 -0.25 0.50

COEF DECAY 5.52x105-6.02 0.15

COEF ROOT 33.43 -1.23 0.27

H&P ERREST 7.93x1016 -28.21 0.066

NEXT3P 2.19x1012 -18.60 0.087

NLP 1.80x108-10.39 0.12

PRIOR2P 3.58x105-6.34 0.14

REFSOLN EDGE 1.13x104-3.33 0.23

REFSOLN ELEM 262.43 -0.90 0.39

SMOOTH PRED 9.60 -0.33 0.43

T3S 5.10x106-5.99 0.18

TYPEPARAM 6.02x103-1.99 0.29

Table 33: Parameters of the least squares fit for

||ehp||E = AeBNC

dof for the mild peak problem.

strategy factor

REFSOLN EDGE 1.00

REFSOLN ELEM 1.13

APRIORI 1.29

TYPEPARAM 1.38

NEXT3P 1.51

H&P ERREST 1.52

NLP 1.92

T3S 2.02

COEF ROOT 2.13

PRIOR2P 2.26

SMOOTH PRED 2.45

COEF DECAY 2.88

ALTERNATE 4.11

Table 34: Factor by which N is larger than the best

strategy for the mild peak problem at low accuracy,

1.0x10−2.

strategy A B

ALTERNATE 2.23 -0.42

APRIORI 2.16x103-1.41

COEF DECAY 2.53 -0.52

COEF ROOT 3.73 -0.59

H&P ERREST 0.56 -0.53

NEXT3P 0.95 -0.58

NLP 1.32 -0.57

PRIOR2P 1.58 -0.51

REFSOLN EDGE 35.07 -1.07

REFSOLN ELEM 2.26x103-1.52

SMOOTH PRED 271.26 -0.96

T3S 28.24 -0.84

TYPEPARAM 760.49 -1.29

Table 35: Parameters of the least squares fit for

||ehp||E = AeBN1/3

dof for the mild peak problem.

strategy factor

REFSOLN ELEM 1.00

APRIORI 1.25

TYPEPARAM 1.37

REFSOLN EDGE 1.47

T3S 2.88

SMOOTH PRED 2.91

NEXT3P 4.19

H&P ERREST 4.66

NLP 4.88

COEF ROOT 5.67

PRIOR2P 7.09

COEF DECAY 7.60

ALTERNATE 14.36

Table 36: Factor by which N is larger than the best

strategy for the mild peak problem at high accuracy,

1.0x10−6.

98
Figure 272: The solution of the sharp peak problem.

5.10 Sharp Peak

This is the hard version of the peak problem (Section 5.9) with α = 100000 and (xc, yc) = (.51, .117). We

used τ = 10−5for the grid images. The APRIORI strategy refines by h if the element touches the center of

the peak and by p otherwise.

99
Figure 273: Example grid for the ALTERNATE

strategy with the sharp peak problem, including details at the peak.

Figure 274: Example grid for the APRIORI strategy

with the sharp peak problem, including details at the

peak.

Figure 275: Example grid for the COEF DECAY

strategy with the sharp peak problem, including details at the peak.

Figure 276: Example grid for the COEF ROOT

strategy with the sharp peak problem, including details at the peak.

Figure 277: Example grid for the H&P ERREST

strategy with the sharp peak problem, including details at the peak.

Figure 278: Example grid for the NEXT3P strategy

with the sharp peak problem, including details at the

peak.

Figure 279: Example grid for the NLP strategy with

the sharp peak problem, including details at the peak.

Figure 280: Example grid for the PRIOR2P strategy

with the sharp peak problem, including details at the

peak.

100
Figure 281: Example grid for the REFSOLN EDGE

strategy with the sharp peak problem, including details at the peak.

Figure 282: Example grid for the REFSOLN ELEM

strategy with the sharp peak problem, including details at the peak.

Figure 283: Example grid for the SMOOTH PRED

strategy with the sharp peak problem, including details at the peak.

Figure 284: Example grid for the T3S strategy with

the sharp peak problem, including details at the peak.

Figure 285: Example grid for the TYPEPARAM

strategy with the sharp peak problem, including details at the peak.

Figure 286: Log-Log plot of the convergence of the

ALTERNATE strategy with the sharp peak problem.

101
Figure 287: Log-Log plot of the convergence of the

APRIORI strategy with the sharp peak problem.

Figure 288: Log-Log plot of the convergence of the

COEF DECAY strategy with the sharp peak problem.

Figure 289: Log-Log plot of the convergence of the

COEF ROOT strategy with the sharp peak problem.

Figure 290: Log-Log plot of the convergence of the

H&P ERREST strategy with the sharp peak problem.

102
Figure 291: Log-Log plot of the convergence of the

NEXT3P strategy with the sharp peak problem.

Figure 292: Log-Log plot of the convergence of the

NLP strategy with the sharp peak problem.

Figure 293: Log-Log plot of the convergence of the

PRIOR2P strategy with the sharp peak problem.

Figure 294: Log-Log plot of the convergence

of the REFSOLN EDGE strategy with the sharp

peak problem.

103
Figure 295: Log-Log plot of the convergence

of the REFSOLN ELEM strategy with the sharp

peak problem.

Figure 296: Log-Log plot of the convergence of the

SMOOTH PRED strategy with the sharp peak problem.

Figure 297: Log-Log plot of the convergence of the

T3S strategy with the sharp peak problem.

Figure 298: Log-Log plot of the convergence of the

TYPEPARAM strategy with the sharp peak problem.

104
Figure 299: Log-Log plot of the convergence of all strategies with the sharp peak problem.

105
strategy A B C

ALTERNATE 15.36 -0.86 0.29

APRIORI 18.05 -0.30 0.41

COEF DECAY 5.19x1010 -14.80 0.097

COEF ROOT 38.27 -1.17 0.28

H&P ERREST 2.05x1030 -49.20 0.058

NEXT3P 1.84x1035 -65.99 0.038

NLP 6.52x1035 -41.09 0.093

PRIOR2P 400.63 -2.36 0.21

REFSOLN EDGE 2.19x107-6.65 0.18

REFSOLN ELEM 2.05x1034 -56.36 0.061

SMOOTH PRED 0.76 -0.055 0.53

T3S 9.11x1035 -41.24 0.098

TYPEPARAM 8.81 -0.16 0.55

Table 37: Parameters of the least squares fit for

||ehp||E = AeBNC

dof for the sharp peak problem.

strategy factor

REFSOLN EDGE 1.00

REFSOLN ELEM 1.12

TYPEPARAM 1.59

NEXT3P 1.73

COEF DECAY 1.90

PRIOR2P 1.96

COEF ROOT 1.98

H&P ERREST 2.23

ALTERNATE 3.13

T3S 3.73

APRIORI 4.15

NLP 5.67

SMOOTH PRED 6.06

Table 38: Factor by which N is larger than the best

strategy for the sharp peak problem at low accuracy,

1.0x10−2.

strategy A B

ALTERNATE 2.29 -0.46

APRIORI 370.62 -0.77

COEF DECAY 1.19 -0.52

COEF ROOT 4.32 -0.59

H&P ERREST 22.70 -0.77

NEXT3P 0.88 -0.53

NLP 4.47x106-1.35

PRIOR2P 1.54 -0.51

REFSOLN EDGE 166.16 -1.18

REFSOLN ELEM 627.71 -1.30

SMOOTH PRED 94.68 -0.60

T3S 3.34x107-1.69

TYPEPARAM 1.34x104-1.43

Table 39: Parameters of the least squares fit for

||ehp||E = AeBN1/3

dof for the sharp peak problem.

strategy factor

REFSOLN ELEM 1.00

REFSOLN EDGE 1.11

TYPEPARAM 1.21

T3S 1.67

NLP 2.70

H&P ERREST 2.71

NEXT3P 4.06

APRIORI 4.66

COEF ROOT 4.75

COEF DECAY 5.06

PRIOR2P 5.89

SMOOTH PRED 8.22

ALTERNATE 8.62

Table 40: Factor by which N is larger than the best

strategy for the sharp peak problem at high accuracy,

1.0x10−6.

106
Figure 300: The solution of the battery problem.

Figure 301: The initial grid for the battery problem.

5.11 Battery

The battery problem is from a model of heat conduction in a battery with nonhomogeneous materials. It

has piecewise constant coefficients and right hand side, and mixed boundary conditions on a rectangular

domain. The initial grid, shown in Figure 301, is aligned to the discontinuities in the data. The solution

has several point singularities in the interior of the domain where three or more materials meet. See [21] for

further details. The exact solution of this problem is not known, so the error estimate η (Section 3) is used

for the convergence results instead of the error. For the grid images, we used τ = 10−2for most strategies,

and τ = 10−1for COEF ROOT, REFSOLN EDGE and TYPEPARAM. The APRIORI strategy refines by

h if the element touches any of the singularities, and by p otherwise.

107
Figure 302: Example grid for the ALTERNATE

strategy with the battery problem.

Figure 303: Example grid for the APRIORI strategy

with the battery problem.

Figure 304: Example grid for the COEF DECAY

strategy with the battery problem.

Figure 305: Example grid for the COEF ROOT

strategy with the battery problem.

Figure 306: Example grid for the H&P ERREST

strategy with the battery problem.

Figure 307: Example grid for the NEXT3P strategy

with the battery problem.

108
Figure 308: Example grid for the NLP strategy with

the battery problem.

Figure 309: Example grid for the PRIOR2P strategy

with the battery problem.

Figure 310: Example grid for the REFSOLN EDGE

strategy with the battery problem.

Figure 311: Example grid for the REFSOLN ELEM

strategy with the battery problem.

Figure 312: Example grid for the SMOOTH PRED

strategy with the battery problem.

Figure 313: Example grid for the T3S strategy with

the battery problem.

109
Figure 314: Example grid for the TYPEPARAM

strategy with the battery problem.

Figure 315: Log-Log plot of the convergence of the

ALTERNATE strategy with the battery problem.

Figure 316: Log-Log plot of the convergence of the

APRIORI strategy with the battery problem.

Figure 317: Log-Log plot of the convergence of the

COEF DECAY strategy with the battery problem.

110
Figure 318: Log-Log plot of the convergence of the

COEF ROOT strategy with the battery problem.

Figure 319: Log-Log plot of the convergence of the

H&P ERREST strategy with the battery problem.

Figure 320: Log-Log plot of the convergence of the

NEXT3P strategy with the battery problem.

Figure 321: Log-Log plot of the convergence of the

NLP strategy with the battery problem.

111
Figure 322: Log-Log plot of the convergence of the

PRIOR2P strategy with the battery problem.

Figure 323: Log-Log plot of the convergence of the

REFSOLN EDGE strategy with the battery problem.

Figure 324: Log-Log plot of the convergence of the

REFSOLN ELEM strategy with the battery problem.

Figure 325: Log-Log plot of the convergence of the

SMOOTH PRED strategy with the battery problem.

112
Figure 326: Log-Log plot of the convergence of the

T3S strategy with the battery problem.

Figure 327: Log-Log plot of the convergence of the

TYPEPARAM strategy with the battery problem.

113
Figure 328: Log-Log plot of the convergence of all strategies with the battery problem.

114
strategy A B C

ALTERNATE 7.91 -0.91 0.21

APRIORI 4.58x1034 -75.15 0.014

COEF DECAY 93.28 -4.06 0.10

COEF ROOT 0.56 -0.041 0.42

H&P ERREST 1.44x104-8.18 0.074

NEXT3P 3.19x104-9.25 0.061

NLP 10.52 -1.70 0.16

PRIOR2P 1.20x103-6.44 0.074

REFSOLN EDGE 0.15 -0.011 0.53

REFSOLN ELEM 4.83 -1.86 0.15

SMOOTH PRED 71.25 -3.15 0.12

T3S 1.80x105-10.13 0.062

TYPEPARAM 0.66 -0.22 0.25

Table 41: Parameters of the least squares fit for

||ehp||E = AeBNC

dof for the battery problem.

strategy factor

H&P ERREST 1.00

REFSOLN ELEM 1.39

NEXT3P 1.68

COEF DECAY 1.78

APRIORI 1.89

PRIOR2P 1.89

T3S 1.94

SMOOTH PRED 2.66

NLP 3.17

ALTERNATE 8.56

REFSOLN EDGE 19.22

COEF ROOT 31.82

TYPEPARAM 92.09

Table 42: Factor by which N is larger than the best

strategy for the battery problem at low accuracy,

1.0x10−2.

strategy A B

ALTERNATE 0.48 -0.15

APRIORI 0.59 -0.23

COEF DECAY 0.090 -0.12

COEF ROOT 1.25 -0.13

H&P ERREST 0.079 -0.15

NEXT3P 0.10 -0.12

NLP 0.11 -0.14

PRIOR2P 0.087 -0.11

REFSOLN EDGE 0.37 -0.12

REFSOLN ELEM 0.11 -0.16

SMOOTH PRED 0.13 -0.14

T3S 0.050 -0.10

TYPEPARAM 0.34 -0.063

Table 43: Parameters of the least squares fit for

||ehp||E = AeBN1/3

dof for the battery problem.

strategy factor

H&P ERREST 1.00

REFSOLN ELEM 1.34

APRIORI 1.59

NLP 2.10

T3S 2.11

SMOOTH PRED 2.12

COEF DECAY 2.19

NEXT3P 2.56

PRIOR2P 3.12

ALTERNATE 3.81

REFSOLN EDGE 5.97

COEF ROOT 8.97

TYPEPARAM 61.73

Table 44: Factor by which N is larger than the best

strategy for the battery problem at high accuracy,

5.0x10−4.

115
Figure 329: The solution of the mild boundary layer problem.

5.12 Boundary Layer, Mild

The boundary layer problem is a convection-diffusion equation with first order terms and Dirichlet boundary

conditions on (−1, 1) × (−1, 1). The solution is

(1 − e

−(1−x)/ǫ)(1 − e−(1−y)/ǫ) cos(π(x + y))

where ǫ controls the strength of the boundary layer. In the easy form of this problem we use ǫ = 10−1. For

the grid images, τ = 10−4. In the APRIORI strategy we refine by h if the element touches either of the

boundaries with a boundary layer, and by p otherwise.

116
Figure 330: Example grid for the ALTERNATE

strategy with the mild boundary layer problem.

Figure 331: Example grid for the APRIORI strategy

with the mild boundary layer problem.

Figure 332: Example grid for the COEF DECAY

strategy with the mild boundary layer problem.

Figure 333: Example grid for the COEF ROOT

strategy with the mild boundary layer problem.

Figure 334: Example grid for the H&P ERREST

strategy with the mild boundary layer problem.

Figure 335: Example grid for the NEXT3P strategy

with the mild boundary layer problem.

117
Figure 336: Example grid for the NLP strategy with

the mild boundary layer problem.

Figure 337: Example grid for the PRIOR2P strategy

with the mild boundary layer problem.

Figure 338: Example grid for the REFSOLN EDGE

strategy with the mild boundary layer problem.

Figure 339: Example grid for the REFSOLN ELEM

strategy with the mild boundary layer problem.

Figure 340: Example grid for the SMOOTH PRED

strategy with the mild boundary layer problem.

Figure 341: Example grid for the T3S strategy with

the mild boundary layer problem.

118
Figure 342: Example grid for the TYPEPARAM

strategy with the mild boundary layer problem.

Figure 343: Log-Log plot of the convergence of

the ALTERNATE strategy with the mild boundary

layer problem.

Figure 344: Log-Log plot of the convergence of

the APRIORI strategy with the mild boundary

layer problem.

Figure 345: Log-Log plot of the convergence of

the COEF DECAY strategy with the mild boundary

layer problem.

119
Figure 346: Log-Log plot of the convergence of

the COEF ROOT strategy with the mild boundary

layer problem.

Figure 347: Log-Log plot of the convergence of

the H&P ERREST strategy with the mild boundary

layer problem.

Figure 348: Log-Log plot of the convergence of

the NEXT3P strategy with the mild boundary

layer problem.

Figure 349: Log-Log plot of the convergence of the

NLP strategy with the mild boundary layer problem.

120
Figure 350: Log-Log plot of the convergence of

the PRIOR2P strategy with the mild boundary

layer problem.

Figure 351: Log-Log plot of the convergence of the

REFSOLN EDGE strategy with the mild boundary

layer problem.

Figure 352: Log-Log plot of the convergence of the

REFSOLN ELEM strategy with the mild boundary

layer problem.

Figure 353: Log-Log plot of the convergence of the

SMOOTH PRED strategy with the mild boundary

layer problem.

121
Figure 354: Log-Log plot of the convergence of the

T3S strategy with the mild boundary layer problem.

Figure 355: Log-Log plot of the convergence of

the TYPEPARAM strategy with the mild boundary

layer problem.

122
Figure 356: Log-Log plot of the convergence of all strategies with the mild boundary layer problem.

123
strategy A B C

ALTERNATE 2.06x105-4.10 0.17

APRIORI 8.34x1032 -69.02 0.019

COEF DECAY 31.86 -0.76 0.33

COEF ROOT 90.23 -1.40 0.25

H&P ERREST 1.69x1024 -44.04 0.045

NEXT3P 1.11x105-5.30 0.16

NLP 90.72 -1.30 0.27

PRIOR2P 9.46x104-5.24 0.16

REFSOLN EDGE 3.88 -0.11 0.55

REFSOLN ELEM 4.69 -0.21 0.46

SMOOTH PRED 2.50 -0.050 0.62

T3S 1.89x1018 -19.72 0.10

TYPEPARAM 3.24 -0.087 0.59

Table 45: Parameters of the least squares fit for

||ehp||E = AeBNC

dof for the mild boundary layer problem.

strategy factor

H&P ERREST 1.00

TYPEPARAM 1.02

REFSOLN EDGE 1.08

NEXT3P 1.14

PRIOR2P 1.14

COEF DECAY 1.18

NLP 1.25

COEF ROOT 1.30

REFSOLN ELEM 1.35

SMOOTH PRED 1.59

ALTERNATE 2.82

T3S 3.13

APRIORI 3.20

Table 46: Factor by which N is larger than the best

strategy for the mild boundary layer problem at low

accuracy, 1.0x10−2.

strategy A B

ALTERNATE 4.63 -0.44

APRIORI 0.065 -0.14

COEF DECAY 23.90 -0.69

COEF ROOT 4.34 -0.53

H&P ERREST 0.22 -0.38

NEXT3P 1.35 -0.47

NLP 7.50 -0.57

PRIOR2P 1.58 -0.48

REFSOLN EDGE 2.01x103-1.11

REFSOLN ELEM 177.13 -0.83

SMOOTH PRED 9.54x103-1.10

T3S 607.31 -0.73

TYPEPARAM 4.14x103-1.21

Table 47: Parameters of the least squares fit for

||ehp||E = AeBN1/3

dof for the mild boundary layer problem.

strategy factor

TYPEPARAM 1.00

REFSOLN EDGE 1.15

SMOOTH PRED 1.51

REFSOLN ELEM 1.96

COEF DECAY 2.41

NLP 3.38

T3S 3.42

COEF ROOT 3.97

NEXT3P 4.05

PRIOR2P 4.14

H&P ERREST 4.75

ALTERNATE 6.80

APRIORI 219.71

Table 48: Factor by which N is larger than the best

strategy for the mild boundary layer problem at high

accuracy, 1.0x10−6.

124
Figure 357: The solution of the strong boundary layer problem.

5.13 Boundary Layer, Strong

For the hard version of the boundary layer problem (Section 5.12) we use ǫ = 10−3. For the grid images,

τ = 10−1. In the APRIORI strategy we refine by h if the element touches either of the boundaries with a

boundary layer, and by p otherwise.

125
Figure 358: Example grid for the ALTERNATE

strategy with the strong boundary layer problem.

Figure 359: Example grid for the APRIORI strategy

with the strong boundary layer problem.

Figure 360: Example grid for the COEF DECAY

strategy with the strong boundary layer problem.

Figure 361: Example grid for the COEF ROOT

strategy with the strong boundary layer problem.

Figure 362: Example grid for the H&P ERREST

strategy with the strong boundary layer problem.

Figure 363: Example grid for the NEXT3P strategy

with the strong boundary layer problem.

126
Figure 364: Example grid for the NLP strategy with

the strong boundary layer problem.

Figure 365: Example grid for the PRIOR2P strategy

with the strong boundary layer problem.

Figure 366: Example grid for the REFSOLN EDGE

strategy with the strong boundary layer problem.

Figure 367: Example grid for the REFSOLN ELEM

strategy with the strong boundary layer problem.

Figure 368: Example grid for the SMOOTH PRED

strategy with the strong boundary layer problem.

Figure 369: Example grid for the T3S strategy with

the strong boundary layer problem.

127
Figure 370: Example grid for the TYPEPARAM

strategy with the strong boundary layer problem.

Figure 371: Log-Log plot of the convergence of the

ALTERNATE strategy with the strong boundary

layer problem.

Figure 372: Log-Log plot of the convergence of

the APRIORI strategy with the strong boundary

layer problem.

Figure 373: Log-Log plot of the convergence of the

COEF DECAY strategy with the strong boundary

layer problem.

128
Figure 374: Log-Log plot of the convergence of the

COEF ROOT strategy with the strong boundary

layer problem.

Figure 375: Log-Log plot of the convergence of the

H&P ERREST strategy with the strong boundary

layer problem.

Figure 376: Log-Log plot of the convergence of

the NEXT3P strategy with the strong boundary

layer problem.

Figure 377: Log-Log plot of the convergence of the

NLP strategy with the strong boundary layer problem.

129
Figure 378: Log-Log plot of the convergence of

the PRIOR2P strategy with the strong boundary

layer problem.

Figure 379: Log-Log plot of the convergence of the

REFSOLN EDGE strategy with the strong boundary

layer problem.

Figure 380: Log-Log plot of the convergence of the

REFSOLN ELEM strategy with the strong boundary

layer problem.

Figure 381: Log-Log plot of the convergence of the

SMOOTH PRED strategy with the strong boundary

layer problem.

130
Figure 382: Log-Log plot of the convergence of the

T3S strategy with the strong boundary layer problem.

Figure 383: Log-Log plot of the convergence of the

TYPEPARAM strategy with the strong boundary

layer problem.

131
Figure 384: Log-Log plot of the convergence of all strategies with the strong boundary layer problem.

132
strategy A B C

ALTERNATE 0.62 -2.40x10−3 0.70

APRIORI 1.67x1033 -64.08 0.018

COEF DECAY 126.02 -0.33 0.28

COEF ROOT 33.06 -0.22 0.30

H&P ERREST 20.03 -0.22 0.30

NEXT3P 874.53 -0.31 0.32

NLP 1.43x1032 -64.00 0.018

PRIOR2P 2.74 -0.052 0.39

REFSOLN EDGE 22.11 -0.085 0.43

REFSOLN ELEM 3.99x1034 -42.08 0.062

SMOOTH PRED 2.71 -2.52x10−3 0.67

T3S 17.85 -0.44 0.26

TYPEPARAM 1.20x1034 -49.03 0.046

Table 49: Parameters of the least squares fit

for ||ehp||E = AeBNC

dof for the strong boundary

layer problem.

strategy factor

REFSOLN EDGE 1.00

ALTERNATE 1.11

T3S 1.64

NEXT3P 1.87

REFSOLN ELEM 1.93

TYPEPARAM 2.76

SMOOTH PRED 2.93

NLP 2.99

H&P ERREST 3.71

COEF DECAY 4.17

COEF ROOT 4.54

PRIOR2P 4.55

APRIORI 13.73

Table 50: Factor by which N is larger than the best

strategy for the strong boundary layer problem at low

accuracy, 1.0x10−2.

strategy A B

ALTERNATE 1.74x103-0.36

APRIORI 0.22 -0.038

COEF DECAY 15.86 -0.14

COEF ROOT 10.56 -0.13

H&P ERREST 7.67 -0.13

NEXT3P 578.00 -0.27

NLP 0.16 -0.060

PRIOR2P 12.41 -0.13

REFSOLN EDGE 676.92 -0.34

REFSOLN ELEM 3.04x104-0.36

SMOOTH PRED 2.82x104-0.32

T3S 1.91 -0.14

TYPEPARAM 40.03 -0.18

Table 51: Parameters of the least squares fit

for ||ehp||E = AeBN1/3

dof for the strong boundary

layer problem.

strategy factor

ALTERNATE 1.00

REFSOLN EDGE 1.07

REFSOLN ELEM 1.75

NEXT3P 2.00

SMOOTH PRED 2.15

TYPEPARAM 4.67

T3S 6.25

COEF DECAY 7.93

H&P ERREST 8.78

PRIOR2P 9.40

COEF ROOT 9.74

NLP 257.52

APRIORI 926.79

Table 52: Factor by which N is larger than the best

strategy for the strong boundary layer problem at

high accuracy, 1.0x10−6.

133
Figure 385: The solution of the mild oscillatory problem.

5.14 Oscillatory, Mild

The oscillatory problem contains several circular waves which get closer together as you approach the origin.

The PDE is a Helmholtz equation with Dirichlet boundary conditions on the unit square. The solution is

sin( 1

α + r

)

where r =

p

x

2 + y2. The number of oscillations, N, is determined by the parameter α =

1

Nπ . For the

easy form of this problem we use N = 10.5. τ = 10−3for the grid images. For APRIORI, refine by h if

the element touches the origin and by p otherwise. In the perspective view of the solution in Figure 385 we

zoomed in on the origin to show the details of the oscillations.

134
Figure 386: Example grid for the ALTERNATE

strategy with the mild oscillatory problem, including

details at the origin.

Figure 387: Example grid for the APRIORI strategy

with the mild oscillatory problem, including details

at the origin.

Figure 388: Example grid for the COEF DECAY

strategy with the mild oscillatory problem, including

details at the origin.

Figure 389: Example grid for the COEF ROOT

strategy with the mild oscillatory problem, including

details at the origin.

Figure 390: Example grid for the H&P ERREST

strategy with the mild oscillatory problem, including

details at the origin.

Figure 391: Example grid for the NEXT3P strategy

with the mild oscillatory problem, including details

at the origin.

Figure 392: Example grid for the NLP strategy with

the mild oscillatory problem, including details at the

origin.

Figure 393: Example grid for the PRIOR2P strategy

with the mild oscillatory problem, including details

at the origin.

135
Figure 394: Example grid for the REFSOLN EDGE

strategy with the mild oscillatory problem, including

details at the origin.

Figure 395: Example grid for the REFSOLN ELEM

strategy with the mild oscillatory problem, including

details at the origin.

Figure 396: Example grid for the SMOOTH PRED

strategy with the mild oscillatory problem, including

details at the origin.

Figure 397: Example grid for the T3S strategy with

the mild oscillatory problem, including details at the

origin.

Figure 398: Example grid for the TYPEPARAM

strategy with the mild oscillatory problem, including

details at the origin.

Figure 399: Log-Log plot of the convergence of

the ALTERNATE strategy with the mild oscillatory problem.

136
Figure 400: Log-Log plot of the convergence of the

APRIORI strategy with the mild oscillatory problem.

Figure 401: Log-Log plot of the convergence of

the COEF DECAY strategy with the mild oscillatory problem.

Figure 402: Log-Log plot of the convergence of

the COEF ROOT strategy with the mild oscillatory problem.

Figure 403: Log-Log plot of the convergence of

the H&P ERREST strategy with the mild oscillatory problem.

137
Figure 404: Log-Log plot of the convergence of the

NEXT3P strategy with the mild oscillatory problem.

Figure 405: Log-Log plot of the convergence of the

NLP strategy with the mild oscillatory problem.

Figure 406: Log-Log plot of the convergence of the

PRIOR2P strategy with the mild oscillatory problem.

Figure 407: Log-Log plot of the convergence of the

REFSOLN EDGE strategy with the mild oscillatory problem.

138
Figure 408: Log-Log plot of the convergence of the

REFSOLN ELEM strategy with the mild oscillatory problem.

Figure 409: Log-Log plot of the convergence of

the SMOOTH PRED strategy with the mild oscillatory problem.

Figure 410: Log-Log plot of the convergence of the

T3S strategy with the mild oscillatory problem.

Figure 411: Log-Log plot of the convergence of

the TYPEPARAM strategy with the mild oscillatory problem.

139
Figure 412: Log-Log plot of the convergence of all strategies with the mild oscillatory problem.

140
strategy A B C

ALTERNATE 486.12 -0.66 0.29

APRIORI 20.77 -0.17 0.51

COEF DECAY 10.88 -0.100 0.48

COEF ROOT 0.79 -8.68x10−3 0.63

H&P ERREST 9.40x1035 -69.23 0.027

NEXT3P 6.91 -1.07 0.23

NLP 11.92 -0.032 0.60

PRIOR2P 4.13 -0.15 0.39

REFSOLN EDGE 2.17x1014 -14.63 0.12

REFSOLN ELEM 15.08 -0.13 0.54

SMOOTH PRED 23.96 -0.044 0.61

T3S 202.82 -0.90 0.30

TYPEPARAM 1.47x1034 -54.41 0.055

Table 53: Parameters of the least squares fit for

||ehp||E = AeBNC

dof for the mild oscillatory problem.

strategy factor

APRIORI 1.00

REFSOLN ELEM 1.16

REFSOLN EDGE 1.48

TYPEPARAM 1.48

T3S 1.73

NEXT3P 1.82

SMOOTH PRED 3.12

H&P ERREST 4.13

COEF DECAY 4.83

NLP 5.29

PRIOR2P 8.48

ALTERNATE 10.98

COEF ROOT 11.52

Table 54: Factor by which N is larger than the best

strategy for the mild oscillatory problem at low accuracy, 1.0x10−2

.

strategy A B

ALTERNATE 59.42 -0.34

APRIORI 1.92x104-1.23

COEF DECAY 899.51 -0.58

COEF ROOT 775.77 -0.43

H&P ERREST 0.12 -0.16

NEXT3P 0.17 -0.23

NLP 7.42x104-0.78

PRIOR2P 19.89 -0.32

REFSOLN EDGE 784.24 -0.86

REFSOLN ELEM 7.16x103-1.11

SMOOTH PRED 1.96x105-1.00

T3S 47.56 -0.62

TYPEPARAM 187.66 -0.77

Table 55: Parameters of the least squares fit for

||ehp||E = AeBN1/3

dof for the mild oscillatory problem.

strategy factor

APRIORI 1.00

REFSOLN ELEM 1.12

REFSOLN EDGE 1.91

TYPEPARAM 2.15

SMOOTH PRED 2.42

T3S 3.23

NLP 4.58

COEF DECAY 6.06

COEF ROOT 14.78

NEXT3P 18.81

PRIOR2P 19.79

ALTERNATE 20.32

H&P ERREST 38.23

Table 56: Factor by which N is larger than the best

strategy for the mild oscillatory problem at high accuracy, 1.0x10−6

.

141
Figure 413: The solution of the strong oscillatory problem.

5.15 Oscillatory, Strong

For the strong version of the oscillatory problem (Section 5.14) we use N = 50.5. τ = 10−2for the grid

images. For APRIORI, refine by h if the element touches the origin and by p otherwise.

142
Figure 414: Example grid for the ALTERNATE

strategy with the strong oscillatory problem, including details at the origin.

Figure 415: Example grid for the APRIORI strategy

with the strong oscillatory problem, including details

at the origin.

Figure 416: Example grid for the COEF DECAY

strategy with the strong oscillatory problem, including details at the origin.

Figure 417: Example grid for the COEF ROOT

strategy with the strong oscillatory problem, including details at the origin.

Figure 418: Example grid for the H&P ERREST

strategy with the strong oscillatory problem, including details at the origin.

Figure 419: Example grid for the NEXT3P strategy

with the strong oscillatory problem, including details

at the origin.

Figure 420: Example grid for the NLP strategy with

the strong oscillatory problem, including details at

the origin.

Figure 421: Example grid for the PRIOR2P strategy

with the strong oscillatory problem, including details

at the origin.

143
Figure 422: Example grid for the REFSOLN EDGE

strategy with the strong oscillatory problem, including details at the origin.

Figure 423: Example grid for the REFSOLN ELEM

strategy with the strong oscillatory problem, including details at the origin.

Figure 424: Example grid for the SMOOTH PRED

strategy with the strong oscillatory problem, including details at the origin.

Figure 425: Example grid for the T3S strategy with

the strong oscillatory problem, including details at

the origin.

Figure 426: Example grid for the TYPEPARAM

strategy with the strong oscillatory problem, including details at the origin.

Figure 427: Log-Log plot of the convergence of

the ALTERNATE strategy with the strong oscillatory problem.

144
Figure 428: Log-Log plot of the convergence of the

APRIORI strategy with the strong oscillatory problem.

Figure 429: Log-Log plot of the convergence of

the COEF DECAY strategy with the strong oscillatory problem.

Figure 430: Log-Log plot of the convergence of

the COEF ROOT strategy with the strong oscillatory problem.

Figure 431: Log-Log plot of the convergence of

the H&P ERREST strategy with the strong oscillatory problem.

145
Figure 432: Log-Log plot of the convergence of the

NEXT3P strategy with the strong oscillatory problem.

Figure 433: Log-Log plot of the convergence of the

NLP strategy with the strong oscillatory problem.

Figure 434: Log-Log plot of the convergence of the

PRIOR2P strategy with the strong oscillatory problem.

Figure 435: Log-Log plot of the convergence of the

REFSOLN EDGE strategy with the strong oscillatory problem.

146
Figure 436: Log-Log plot of the convergence of the

REFSOLN ELEM strategy with the strong oscillatory problem.

Figure 437: Log-Log plot of the convergence of the

SMOOTH PRED strategy with the strong oscillatory problem.

Figure 438: Log-Log plot of the convergence of the

T3S strategy with the strong oscillatory problem.

Figure 439: Log-Log plot of the convergence of

the TYPEPARAM strategy with the strong oscillatory problem.

147
Figure 440: Log-Log plot of the convergence of all strategies with the strong oscillatory problem.

148
strategy A B C

ALTERNATE 7.11x1032 -35.32 0.054

APRIORI 4.11x1013 -10.82 0.13

COEF DECAY 3.38 -3.09x10−3 0.62

COEF ROOT 1.82 -6.87x10−4 0.69

H&P ERREST 5.31x1013 -22.33 0.046

NEXT3P 7.83x1031 -64.98 0.020

NLP 2.55x1031 -65.75 7.62x10−3

PRIOR2P 1.49x104-1.66 0.17

REFSOLN EDGE 14.32 -5.33x10−3 0.74

REFSOLN ELEM 4.77x106-0.59 0.36

SMOOTH PRED 287.34 -0.24 0.38

T3S 2.03x104-0.19 0.45

TYPEPARAM 3.43x1035 -40.95 0.077

Table 57: Parameters of the least squares fit for

||ehp||E = AeBNC

dof for the strong oscillatory problem.

strategy factor

APRIORI 1.00

T3S 1.45

TYPEPARAM 1.60

REFSOLN EDGE 1.75

REFSOLN ELEM 1.83

SMOOTH PRED 2.55

NEXT3P 2.83

H&P ERREST 9.48

COEF DECAY 22.37

COEF ROOT 51.26

PRIOR2P 52.76

ALTERNATE 458.20

NLP 2.78x106

Table 58: Factor by which N is larger than the best

strategy for the strong oscillatory problem at low accuracy, 1.0x10−3

.

strategy A B

ALTERNATE 1.33x103-0.073

APRIORI 530.95 -0.53

COEF DECAY 6.39x103-0.23

COEF ROOT 1.24x104-0.18

H&P ERREST 0.026 -0.060

NEXT3P 7.27x10−3-0.061

NLP 7.89 -0.027

PRIOR2P 2.18 -0.080

REFSOLN EDGE 2.92x106-0.75

REFSOLN ELEM 2.38x107-0.79

SMOOTH PRED 2.17x103-0.43

T3S 1.14x107-0.83

TYPEPARAM 6.62x104-0.62

Table 59: Parameters of the least squares fit for

||ehp||E = AeBN1/3

dof for the strong oscillatory problem.

strategy factor

T3S 1.00

APRIORI 1.14

REFSOLN EDGE 1.18

REFSOLN ELEM 1.26

TYPEPARAM 1.37

SMOOTH PRED 2.62

COEF DECAY 19.39

COEF ROOT 42.57

NEXT3P 57.15

H&P ERREST 110.63

PRIOR2P 133.66

ALTERNATE 652.42

NLP 5.19x1010

Table 60: Factor by which N is larger than the best

strategy for the strong oscillatory problem at high

accuracy, 1.0x10−6.

149
Figure 441: The solution of the mild wave front problem.

5.16 Wave Front, Mild

The circular wave front problem is often used as an example in adaptive grid refinement papers. It is

Poisson’s equation with Dirichlet boundary conditions on the unit square. The solution is

tan−1(α(r − r0))

where r =

p

(x − xc)

2 + (y − yc)2. The location of the wave front is defined by a circle with radius r0 and

center (xc, yc). α determines the steepness of the wave front. In addition to the wave front, the solution

has a mild singularity at the center of the circle, if the center is located in the closure of the domain. For

the easy form of this problem we use α = 20, (xc, yc) = (−.05, −.05), and r0 = 0.7. The center is chosen

outside the domain so that only the wave front is a factor in the adaptivity, not the singularity. τ = 10−4

for the grid images. For the APRIORI strategy, refine by h if the element touches the circle that defines the

location of the wave front and has degree at least 3 (chosen arbitrarily), and by p otherwise.

150
Figure 442: Example grid for the ALTERNATE

strategy with the mild wave front problem.

Figure 443: Example grid for the APRIORI strategy

with the mild wave front problem.

Figure 444: Example grid for the COEF DECAY

strategy with the mild wave front problem.

Figure 445: Example grid for the COEF ROOT

strategy with the mild wave front problem.

Figure 446: Example grid for the H&P ERREST

strategy with the mild wave front problem.

Figure 447: Example grid for the NEXT3P strategy

with the mild wave front problem.

151
Figure 448: Example grid for the NLP strategy with

the mild wave front problem.

Figure 449: Example grid for the PRIOR2P strategy

with the mild wave front problem.

Figure 450: Example grid for the REFSOLN EDGE

strategy with the mild wave front problem.

Figure 451: Example grid for the REFSOLN ELEM

strategy with the mild wave front problem.

Figure 452: Example grid for the SMOOTH PRED

strategy with the mild wave front problem.

Figure 453: Example grid for the T3S strategy with

the mild wave front problem.

152
Figure 454: Example grid for the TYPEPARAM

strategy with the mild wave front problem.

Figure 455: Log-Log plot of the convergence of

the ALTERNATE strategy with the mild wave

front problem.

Figure 456: Log-Log plot of the convergence of the

APRIORI strategy with the mild wave front problem.

Figure 457: Log-Log plot of the convergence of

the COEF DECAY strategy with the mild wave

front problem.

153
Figure 458: Log-Log plot of the convergence of

the COEF ROOT strategy with the mild wave

front problem.

Figure 459: Log-Log plot of the convergence of

the H&P ERREST strategy with the mild wave

front problem.

Figure 460: Log-Log plot of the convergence of the

NEXT3P strategy with the mild wave front problem.

Figure 461: Log-Log plot of the convergence of the

NLP strategy with the mild wave front problem.

154
Figure 462: Log-Log plot of the convergence of the

PRIOR2P strategy with the mild wave front problem.

Figure 463: Log-Log plot of the convergence of

the REFSOLN EDGE strategy with the mild wave

front problem.

Figure 464: Log-Log plot of the convergence of

the REFSOLN ELEM strategy with the mild wave

front problem.

Figure 465: Log-Log plot of the convergence of

the SMOOTH PRED strategy with the mild wave

front problem.

155
Figure 466: Log-Log plot of the convergence of the

T3S strategy with the mild wave front problem.

Figure 467: Log-Log plot of the convergence of

the TYPEPARAM strategy with the mild wave

front problem.

156
Figure 468: Log-Log plot of the convergence of all strategies with the mild wave front problem.

157
strategy A B C

ALTERNATE 12.84 -1.00 0.26

APRIORI 253.01 -2.60 0.19

COEF DECAY 38.63 -1.47 0.25

COEF ROOT 6.85 -0.88 0.28

H&P ERREST 5.75x107-11.85 0.093

NEXT3P 1.78x104-5.39 0.14

NLP 0.35 -0.018 0.70

PRIOR2P 232.22 -2.76 0.18

REFSOLN EDGE 0.73 -0.12 0.52

REFSOLN ELEM 0.97 -0.12 0.52

SMOOTH PRED 2.95 -0.34 0.40

T3S 2.88 -0.17 0.46

TYPEPARAM 0.74 -0.11 0.52

Table 61: Parameters of the least squares fit for

||ehp||E = AeBNC

dof for the mild wave front problem.

strategy factor

REFSOLN EDGE 1.00

H&P ERREST 1.01

REFSOLN ELEM 1.03

NEXT3P 1.10

COEF DECAY 1.17

APRIORI 1.17

PRIOR2P 1.28

SMOOTH PRED 1.36

TYPEPARAM 1.37

COEF ROOT 1.48

NLP 2.09

ALTERNATE 2.13

T3S 2.24

Table 62: Factor by which N is larger than the best

strategy for the mild wave front problem at low accuracy, 1.0x10−2

.

strategy A B

ALTERNATE 0.75 -0.37

APRIORI 0.53 -0.41

COEF DECAY 1.59 -0.50

COEF ROOT 1.20 -0.43

H&P ERREST 0.14 -0.34

NEXT3P 0.23 -0.37

NLP 136.67 -0.80

PRIOR2P 0.32 -0.35

REFSOLN EDGE 59.61 -0.88

REFSOLN ELEM 84.36 -0.92

SMOOTH PRED 17.97 -0.68

T3S 112.05 -0.73

TYPEPARAM 41.17 -0.77

Table 63: Parameters of the least squares fit for

||ehp||E = AeBN1/3

dof for the mild wave front problem.

strategy factor

REFSOLN ELEM 1.00

REFSOLN EDGE 1.08

TYPEPARAM 1.49

NLP 1.55

SMOOTH PRED 1.85

T3S 2.18

COEF DECAY 2.91

APRIORI 3.88

COEF ROOT 4.22

NEXT3P 4.32

H&P ERREST 4.73

PRIOR2P 5.41

ALTERNATE 6.15

Table 64: Factor by which N is larger than the best

strategy for the mild wave front problem at high accuracy, 1.0x10−6

.

158
Figure 469: The solution of the steep wave front problem.

5.17 Wave Front, Steep

In the hard version of the wave front problem (Section 5.16) the location of the wave front is the same, but it

is much steeper. The parameters are α = 1000, (xc, yc) = (−.05, −.05), and r0 = 0.7. τ = 10−1for the grid

images. For the APRIORI strategy, refine by h if the element touches the circle that defines the location of

the wave front and has degree at least 3 (chosen arbitrarily), and by p otherwise.

159
Figure 470: Example grid for the ALTERNATE

strategy with the steep wave front problem.

Figure 471: Example grid for the APRIORI strategy

with the steep wave front problem.

Figure 472: Example grid for the COEF DECAY

strategy with the steep wave front problem.

Figure 473: Example grid for the COEF ROOT

strategy with the steep wave front problem.

Figure 474: Example grid for the H&P ERREST

strategy with the steep wave front problem.

Figure 475: Example grid for the NEXT3P strategy

with the steep wave front problem.

160
Figure 476: Example grid for the NLP strategy with

the steep wave front problem.

Figure 477: Example grid for the PRIOR2P strategy

with the steep wave front problem.

Figure 478: Example grid for the REFSOLN EDGE

strategy with the steep wave front problem.

Figure 479: Example grid for the REFSOLN ELEM

strategy with the steep wave front problem.

Figure 480: Example grid for the SMOOTH PRED

strategy with the steep wave front problem.

Figure 481: Example grid for the T3S strategy with

the steep wave front problem.

161
Figure 482: Example grid for the TYPEPARAM

strategy with the steep wave front problem.

Figure 483: Log-Log plot of the convergence of

the ALTERNATE strategy with the steep wave

front problem.

Figure 484: Log-Log plot of the convergence of the

APRIORI strategy with the steep wave front problem.

Figure 485: Log-Log plot of the convergence of

the COEF DECAY strategy with the steep wave

front problem.

162
Figure 486: Log-Log plot of the convergence of

the COEF ROOT strategy with the steep wave

front problem.

Figure 487: Log-Log plot of the convergence of

the H&P ERREST strategy with the steep wave

front problem.

Figure 488: Log-Log plot of the convergence of the

NEXT3P strategy with the steep wave front problem.

Figure 489: Log-Log plot of the convergence of the

NLP strategy with the steep wave front problem.

163
Figure 490: Log-Log plot of the convergence of the

PRIOR2P strategy with the steep wave front problem.

Figure 491: Log-Log plot of the convergence of

the REFSOLN EDGE strategy with the steep wave

front problem.

Figure 492: Log-Log plot of the convergence of

the REFSOLN ELEM strategy with the steep wave

front problem.

Figure 493: Log-Log plot of the convergence of

the SMOOTH PRED strategy with the steep wave

front problem.

164
Figure 494: Log-Log plot of the convergence of the

T3S strategy with the steep wave front problem.

Figure 495: Log-Log plot of the convergence of

the TYPEPARAM strategy with the steep wave

front problem.

165
Figure 496: Log-Log plot of the convergence of all strategies with the steep wave front problem.

166
strategy A B C

ALTERNATE 19.59 -0.10 0.39

APRIORI 94.82 -0.70 0.23

COEF DECAY 552.77 -1.23 0.20

COEF ROOT 5.72 -0.33 0.27

H&P ERREST 4.61x105-3.45 0.15

NEXT3P 5.41x105-4.91 0.12

NLP 6.64x1033 -66.67 0.019

PRIOR2P 1.55x104-3.28 0.13

REFSOLN EDGE 1.17 -0.028 0.49

REFSOLN ELEM 9.37 -0.11 0.38

SMOOTH PRED 539.94 -0.97 0.22

T3S 3.98 -0.024 0.48

TYPEPARAM 1.46 -0.023 0.49

Table 65: Parameters of the least squares fit for

||ehp||E = AeBNC

dof for the steep wave front problem.

strategy factor

REFSOLN EDGE 1.00

REFSOLN ELEM 1.45

SMOOTH PRED 1.53

NEXT3P 1.63

COEF DECAY 1.64

H&P ERREST 1.65

PRIOR2P 1.68

TYPEPARAM 1.70

COEF ROOT 1.84

ALTERNATE 1.85

APRIORI 2.00

NLP 2.30

T3S 2.76

Table 66: Factor by which N is larger than the best

strategy for the steep wave front problem at low accuracy, 1.0x10−2

.

strategy A B

ALTERNATE 87.43 -0.23

APRIORI 1.68 -0.13

COEF DECAY 1.26 -0.13

COEF ROOT 0.79 -0.11

H&P ERREST 2.44 -0.15

NEXT3P 0.31 -0.098

NLP 0.19 -0.067

PRIOR2P 0.35 -0.095

REFSOLN EDGE 53.68 -0.26

REFSOLN ELEM 46.81 -0.23

SMOOTH PRED 3.33 -0.16

T3S 82.83 -0.20

TYPEPARAM 74.60 -0.23

Table 67: Parameters of the least squares fit for

||ehp||E = AeBN1/3

dof for the steep wave front problem.

strategy factor

REFSOLN EDGE 1.00

REFSOLN ELEM 1.48

ALTERNATE 1.61

TYPEPARAM 1.61

T3S 2.14

SMOOTH PRED 2.69

H&P ERREST 3.09

COEF DECAY 3.93

APRIORI 4.55

COEF ROOT 5.94

NEXT3P 6.31

PRIOR2P 7.74

NLP 70.96

Table 68: Factor by which N is larger than the best

strategy for the steep wave front problem at high accuracy, 1.0x10−6

.

167
Figure 497: The solution of the asymmetric wave front problem.

5.18 Wave Front, Asymmetric

The asymmetric wave front is similar to the steep wave front except the wave front is not symmetric within

the domain. The parameters are α = 1000, (xc, yc) = (1.5, .25), and r0 = .92. τ = 10−1for the grid images.

For the APRIORI strategy, refine by h if the element touches the circle that defines the location of the wave

front and has degree at least 3 (chosen arbitrarily), and by p otherwise.

168
Figure 498: Example grid for the ALTERNATE

strategy with the asymmetric wave front problem.

Figure 499: Example grid for the APRIORI strategy

with the asymmetric wave front problem.

Figure 500: Example grid for the COEF DECAY

strategy with the asymmetric wave front problem.

Figure 501: Example grid for the COEF ROOT

strategy with the asymmetric wave front problem.

Figure 502: Example grid for the H&P ERREST

strategy with the asymmetric wave front problem.

Figure 503: Example grid for the NEXT3P strategy

with the asymmetric wave front problem.

169
Figure 504: Example grid for the NLP strategy with

the asymmetric wave front problem.

Figure 505: Example grid for the PRIOR2P strategy

with the asymmetric wave front problem.

Figure 506: Example grid for the REFSOLN EDGE

strategy with the asymmetric wave front problem.

Figure 507: Example grid for the REFSOLN ELEM

strategy with the asymmetric wave front problem.

Figure 508: Example grid for the SMOOTH PRED

strategy with the asymmetric wave front problem.

Figure 509: Example grid for the T3S strategy with

the asymmetric wave front problem.

170
Figure 510: Example grid for the TYPEPARAM

strategy with the asymmetric wave front problem.

Figure 511: Log-Log plot of the convergence of the

ALTERNATE strategy with the asymmetric wave

front problem.

Figure 512: Log-Log plot of the convergence of

the APRIORI strategy with the asymmetric wave

front problem.

Figure 513: Log-Log plot of the convergence of the

COEF DECAY strategy with the asymmetric wave

front problem.

171
Figure 514: Log-Log plot of the convergence of the

COEF ROOT strategy with the asymmetric wave

front problem.

Figure 515: Log-Log plot of the convergence of the

H&P ERREST strategy with the asymmetric wave

front problem.

Figure 516: Log-Log plot of the convergence of

the NEXT3P strategy with the asymmetric wave

front problem.

Figure 517: Log-Log plot of the convergence of the

NLP strategy with the asymmetric wave front problem.

172
Figure 518: Log-Log plot of the convergence of

the PRIOR2P strategy with the asymmetric wave

front problem.

Figure 519: Log-Log plot of the convergence of

the REFSOLN EDGE strategy with the asymmetric

wave front problem.

Figure 520: Log-Log plot of the convergence of

the REFSOLN ELEM strategy with the asymmetric

wave front problem.

Figure 521: Log-Log plot of the convergence of the

SMOOTH PRED strategy with the asymmetric wave

front problem.

173
Figure 522: Log-Log plot of the convergence of the

T3S strategy with the asymmetric wave front problem.

Figure 523: Log-Log plot of the convergence of the

TYPEPARAM strategy with the asymmetric wave

front problem.

174
Figure 524: Log-Log plot of the convergence of all strategies with the asymmetric wave front problem.

175
strategy A B C

ALTERNATE 3.07 -0.013 0.53

APRIORI 226.59 -0.89 0.21

COEF DECAY 1.04x104-2.14 0.17

COEF ROOT 7.24 -0.36 0.26

H&P ERREST 2.31x105-2.94 0.16

NEXT3P 4.38x107-7.95 0.093

NLP 0.68 -0.21 0.24

PRIOR2P 1.03x105-4.18 0.12

REFSOLN EDGE 0.80 -0.019 0.51

REFSOLN ELEM 4.85 -0.071 0.41

SMOOTH PRED 1.00x103-1.07 0.21

T3S 16.91 -0.068 0.40

TYPEPARAM 2.65 -0.034 0.46

Table 69: Parameters of the least squares fit

for ||ehp||E = AeBNC

dof for the asymmetric wave

front problem.

strategy factor

REFSOLN EDGE 1.00

REFSOLN ELEM 1.46

NEXT3P 1.52

H&P ERREST 1.63

SMOOTH PRED 1.69

PRIOR2P 1.70

COEF DECAY 1.74

TYPEPARAM 1.77

COEF ROOT 1.86

APRIORI 1.97

ALTERNATE 2.77

T3S 2.96

NLP 6.90

Table 70: Factor by which N is larger than the best

strategy for the asymmetric wave front problem at

low accuracy, 1.0x10−2.

strategy A B

ALTERNATE 227.52 -0.22

APRIORI 1.69 -0.12

COEF DECAY 1.56 -0.13

COEF ROOT 0.83 -0.11

H&P ERREST 4.14 -0.15

NEXT3P 0.24 -0.091

NLP 0.20 -0.045

PRIOR2P 0.44 -0.096

REFSOLN EDGE 31.24 -0.24

REFSOLN ELEM 41.67 -0.21

SMOOTH PRED 4.12 -0.15

T3S 108.10 -0.19

TYPEPARAM 57.80 -0.21

Table 71: Parameters of the least squares fit

for ||ehp||E = AeBN1/3

dof for the asymmetric wave

front problem.

strategy factor

REFSOLN EDGE 1.00

REFSOLN ELEM 1.52

TYPEPARAM 1.64

ALTERNATE 1.88

T3S 2.42

H&P ERREST 2.79

SMOOTH PRED 2.93

COEF DECAY 4.01

APRIORI 4.52

COEF ROOT 5.99

NEXT3P 6.92

PRIOR2P 7.67

NLP 96.23

Table 72: Factor by which N is larger than the best

strategy for the asymmetric wave front problem at

high accuracy, 1.0x10−6.

176
Figure 525: The solution of the singular well problem.

5.19 Singular Well

In the wave front problems of the previous three sections, the center of the circle was placed outside the

domain so the mild singularity at the center of the circle was not a factor. In the singular well problem, the

center of the circle is placed at the center of the domain and the wave front is relatively mild, effectively

creating a well with a mild singularity at the center. α = 50, (xc, yc) = (.5, .5), and r0 = .25. τ = 10−3for

the grid images. For the APRIORI strategy, refine by h if the element touches the circle that defines the

location of the wave front and has degree at least 3 (chosen arbitrarily), or touches the center of the circle,

and by p otherwise.

177
Figure 526: Example grid for the ALTERNATE

strategy with the singular well problem.

Figure 527: Example grid for the APRIORI strategy

with the singular well problem.

Figure 528: Example grid for the COEF DECAY

strategy with the singular well problem.

Figure 529: Example grid for the COEF ROOT

strategy with the singular well problem.

Figure 530: Example grid for the H&P ERREST

strategy with the singular well problem.

Figure 531: Example grid for the NEXT3P strategy

with the singular well problem.

178
Figure 532: Example grid for the NLP strategy with

the singular well problem.

Figure 533: Example grid for the PRIOR2P strategy

with the singular well problem.

Figure 534: Example grid for the REFSOLN EDGE

strategy with the singular well problem.

Figure 535: Example grid for the REFSOLN ELEM

strategy with the singular well problem.

Figure 536: Example grid for the SMOOTH PRED

strategy with the singular well problem.

Figure 537: Example grid for the T3S strategy with

the singular well problem.

179
Figure 538: Example grid for the TYPEPARAM

strategy with the singular well problem.

Figure 539: Log-Log plot of the convergence of the

ALTERNATE strategy with the singular well problem.

Figure 540: Log-Log plot of the convergence of the

APRIORI strategy with the singular well problem.

Figure 541: Log-Log plot of the convergence of the

COEF DECAY strategy with the singular well problem.

180
Figure 542: Log-Log plot of the convergence of the

COEF ROOT strategy with the singular well problem.

Figure 543: Log-Log plot of the convergence of the

H&P ERREST strategy with the singular well problem.

Figure 544: Log-Log plot of the convergence of the

NEXT3P strategy with the singular well problem.

Figure 545: Log-Log plot of the convergence of the

NLP strategy with the singular well problem.

181
Figure 546: Log-Log plot of the convergence of the

PRIOR2P strategy with the singular well problem.

Figure 547: Log-Log plot of the convergence of

the REFSOLN EDGE strategy with the singular

well problem.

Figure 548: Log-Log plot of the convergence of

the REFSOLN ELEM strategy with the singular

well problem.

Figure 549: Log-Log plot of the convergence of

the SMOOTH PRED strategy with the singular

well problem.

182
Figure 550: Log-Log plot of the convergence of the

T3S strategy with the singular well problem.

Figure 551: Log-Log plot of the convergence of the

TYPEPARAM strategy with the singular well problem.

183
Figure 552: Log-Log plot of the convergence of all strategies with the singular well problem.

184
strategy A B C

ALTERNATE 2.01 -0.39 0.30

APRIORI 36.10 -1.26 0.23

COEF DECAY 279.76 -2.27 0.18

COEF ROOT 10.49 -0.92 0.24

H&P ERREST 1.61x1010 -16.68 0.065

NEXT3P 7.76 -0.84 0.25

NLP 3.96x1033 -71.95 0.015

PRIOR2P 428.91 -2.78 0.16

REFSOLN EDGE 2.47 -0.24 0.40

REFSOLN ELEM 0.43 -0.048 0.52

SMOOTH PRED 3.58 -0.33 0.35

T3S 2.72x1018 -31.13 0.052

TYPEPARAM 0.82 -0.16 0.39

Table 73: Parameters of the least squares fit for

||ehp||E = AeBNC

dof for the singular well problem.

strategy factor

REFSOLN EDGE 1.00

T3S 1.28

H&P ERREST 1.36

SMOOTH PRED 1.62

COEF DECAY 1.67

APRIORI 1.69

NEXT3P 1.74

REFSOLN ELEM 1.75

PRIOR2P 1.93

COEF ROOT 2.28

TYPEPARAM 2.40

ALTERNATE 2.69

NLP 2.80

Table 74: Factor by which N is larger than the best

strategy for the singular well problem at low accuracy, 1.0x10−2

.

strategy A B

ALTERNATE 0.82 -0.24

APRIORI 0.56 -0.27

COEF DECAY 0.60 -0.26

COEF ROOT 0.54 -0.23

H&P ERREST 0.093 -0.18

NEXT3P 0.63 -0.26

NLP 0.10 -0.11

PRIOR2P 0.25 -0.20

REFSOLN EDGE 19.52 -0.56

REFSOLN ELEM 24.56 -0.48

SMOOTH PRED 5.38 -0.40

T3S 0.27 -0.26

TYPEPARAM 2.60 -0.31

Table 75: Parameters of the least squares fit for

||ehp||E = AeBN1/3

dof for the singular well problem.

strategy factor

REFSOLN EDGE 1.00

REFSOLN ELEM 1.64

SMOOTH PRED 2.13

T3S 3.62

TYPEPARAM 3.95

APRIORI 4.19

COEF DECAY 4.97

NEXT3P 5.04

ALTERNATE 6.90

COEF ROOT 7.15

PRIOR2P 8.38

H&P ERREST 9.63

NLP 326.76

Table 76: Factor by which N is larger than the best

strategy for the singular well problem at high accuracy, 1.0x10−6

.

185
Figure 553: The solution of the intersecting interfaces problem.

5.20 Intersecting Interfaces

The intersecting interfaces problem has piecewise constant coefficients which create a very strong singularity

at the center of the domain and discontinuous derivatives along the x and y axes. The boundary conditions

are Dirichlet on the domain (−1, 1) × (−1, 1). For the grid images, τ = 5x10−3. For the APRIORI strategy,

refine by h if the element touches the origin and by p otherwise.

186
Figure 554: Example grid for the ALTERNATE

strategy with the intersecting interfaces problem, including details at the singularity.

Figure 555: Example grid for the APRIORI strategy with the intersecting interfaces problem, including details at the singularity.

Figure 556: Example grid for the COEF DECAY

strategy with the intersecting interfaces problem, including details at the singularity.

Figure 557: Example grid for the COEF ROOT

strategy with the intersecting interfaces problem, including details at the singularity.

Figure 558: Example grid for the H&P ERREST

strategy with the intersecting interfaces problem, including details at the singularity.

Figure 559: Example grid for the NEXT3P strategy with the intersecting interfaces problem, including details at the singularity.

Figure 560: Example grid for the NLP strategy with

the intersecting interfaces problem, including details

at the singularity.

Figure 561: Example grid for the PRIOR2P strategy with the intersecting interfaces problem, including details at the singularity.

187
Figure 562: Example grid for the REFSOLN EDGE

strategy with the intersecting interfaces problem, including details at the singularity.

Figure 563: Example grid for the REFSOLN ELEM

strategy with the intersecting interfaces problem, including details at the singularity.

Figure 564: Example grid for the SMOOTH PRED

strategy with the intersecting interfaces problem, including details at the singularity.

Figure 565: Example grid for the T3S strategy with

the intersecting interfaces problem, including details

at the singularity.

Figure 566: Example grid for the TYPEPARAM

strategy with the intersecting interfaces problem, including details at the singularity.

Figure 567: Log-Log plot of the convergence of the

ALTERNATE strategy with the intersecting interfaces problem.

188
Figure 568: Log-Log plot of the convergence of

the APRIORI strategy with the intersecting interfaces problem.

Figure 569: Log-Log plot of the convergence of the

COEF DECAY strategy with the intersecting interfaces problem.

Figure 570: Log-Log plot of the convergence of the

COEF ROOT strategy with the intersecting interfaces problem.

Figure 571: Log-Log plot of the convergence of the

H&P ERREST strategy with the intersecting interfaces problem.

189
Figure 572: Log-Log plot of the convergence of

the NEXT3P strategy with the intersecting interfaces problem.

Figure 573: Log-Log plot of the convergence of the

NLP strategy with the intersecting interfaces problem.

Figure 574: Log-Log plot of the convergence of

the PRIOR2P strategy with the intersecting interfaces problem.

Figure 575: Log-Log plot of the convergence of the

REFSOLN EDGE strategy with the intersecting interfaces problem.

190
Figure 576: Log-Log plot of the convergence of the

REFSOLN ELEM strategy with the intersecting interfaces problem.

Figure 577: Log-Log plot of the convergence of the

SMOOTH PRED strategy with the intersecting interfaces problem.

Figure 578: Log-Log plot of the convergence of the

T3S strategy with the intersecting interfaces problem.

Figure 579: Log-Log plot of the convergence of the

TYPEPARAM strategy with the intersecting interfaces problem.

191
Figure 580: Log-Log plot of the convergence of all strategies with the intersecting interfaces problem.

192
strategy A B C

ALTERNATE 1.95 -0.14 0.29

APRIORI 1.07x103-3.13 0.15

COEF DECAY 22.60 -0.77 0.25

COEF ROOT 31.67 -0.99 0.22

H&P ERREST 3.45 -0.16 0.32

NEXT3P 3.64 -0.14 0.35

NLP 3.58 -0.14 0.34

PRIOR2P 331.68 -2.72 0.13

REFSOLN EDGE 1.56x1033 -70.97 0.014

REFSOLN ELEM 5.46 -0.19 0.37

SMOOTH PRED 4.86 -0.15 0.40

T3S 7.68 -0.71 0.17

TYPEPARAM 199.54 -2.29 0.15

Table 77: Parameters of the least squares fit

for ||ehp||E = AeBNC

dof for the intersecting interfaces problem.

strategy factor

REFSOLN EDGE 1.00

APRIORI 1.08

COEF DECAY 1.71

COEF ROOT 1.83

TYPEPARAM 1.83

PRIOR2P 1.92

SMOOTH PRED 2.35

REFSOLN ELEM 2.41

NEXT3P 5.88

NLP 7.08

H&P ERREST 8.58

ALTERNATE 18.30

T3S 19.15

Table 78: Factor by which N is larger than the best

strategy for the intersecting interfaces problem at low

accuracy, 2.0x10−1.

strategy A B

ALTERNATE 1.47 -0.075

APRIORI 8.29 -0.35

COEF DECAY 6.51 -0.29

COEF ROOT 5.48 -0.27

H&P ERREST 3.12 -0.14

NEXT3P 4.23 -0.18

NLP 3.90 -0.16

PRIOR2P 3.86 -0.23

REFSOLN EDGE 6.68 -0.33

REFSOLN ELEM 7.58 -0.28

SMOOTH PRED 8.59 -0.30

T3S 1.43 -0.061

TYPEPARAM 3.65 -0.23

Table 79: Parameters of the least squares fit

for ||ehp||E = AeBN1/3

dof for the intersecting interfaces problem.

strategy factor

APRIORI 1.00

REFSOLN EDGE 1.47

COEF DECAY 1.56

SMOOTH PRED 1.67

REFSOLN ELEM 1.83

COEF ROOT 1.84

TYPEPARAM 2.32

PRIOR2P 2.63

NEXT3P 5.57

NLP 7.07

H&P ERREST 10.01

ALTERNATE 38.16

T3S 65.48

Table 80: Factor by which N is larger than the best

strategy for the intersecting interfaces problem at

high accuracy, 2.0x10−2.

193
Figure 581: The solution of the multiple difficulties problem.

5.21 Multiple Difficulties

The multiple difficulties problem combines several of the difficulties of the other problems into a single

problem. It contains a reentrant corner point singularity, wave front, peak and boundary layer. For the

selected parameters, the peak falls on the wave front, and the wave front intersects the boundary layer and

point singularity. The parameters are:

• reentrant corner ω = 3π/2

• center of circle for wave front (0, −3/4)

• radius of circle for wave front 3/4

• strength of wave front α = 200

• center of peak (√

5/4, −1/4)

• strength of peak α = 1000

• strength of boundary layer ǫ = 1/100

For the grid images, τ = 10−2. The APRIORI method refines by h in the same cases as it did in the

individual problems.

194
Figure 582: Example grid for the ALTERNATE

strategy with the multiple difficulties problem, including details at the singularity.

Figure 583: Example grid for the APRIORI strategy with the multiple difficulties problem, including

details at the singularity.

Figure 584: Example grid for the COEF DECAY

strategy with the multiple difficulties problem, including details at the singularity.

Figure 585: Example grid for the COEF ROOT

strategy with the multiple difficulties problem, including details at the singularity.

Figure 586: Example grid for the H&P ERREST

strategy with the multiple difficulties problem, including details at the singularity.

Figure 587: Example grid for the NEXT3P strategy

with the multiple difficulties problem, including details at the singularity.

Figure 588: Example grid for the NLP strategy with

the multiple difficulties problem, including details at

the singularity.

Figure 589: Example grid for the PRIOR2P strategy with the multiple difficulties problem, including

details at the singularity.

195
Figure 590: Example grid for the REFSOLN EDGE

strategy with the multiple difficulties problem, including details at the singularity.

Figure 591: Example grid for the REFSOLN ELEM

strategy with the multiple difficulties problem, including details at the singularity.

Figure 592: Example grid for the SMOOTH PRED

strategy with the multiple difficulties problem, including details at the singularity.

Figure 593: Example grid for the T3S strategy with

the multiple difficulties problem, including details at

the singularity.

Figure 594: Example grid for the TYPEPARAM

strategy with the multiple difficulties problem, including details at the singularity.

Figure 595: Log-Log plot of the convergence of the

ALTERNATE strategy with the multiple difficulties problem.

196
Figure 596: Log-Log plot of the convergence of

the APRIORI strategy with the multiple difficulties problem.

Figure 597: Log-Log plot of the convergence of the

COEF DECAY strategy with the multiple difficulties problem.

Figure 598: Log-Log plot of the convergence of the

COEF ROOT strategy with the multiple difficulties problem.

Figure 599: Log-Log plot of the convergence of the

H&P ERREST strategy with the multiple difficulties problem.

197
Figure 600: Log-Log plot of the convergence of the

NEXT3P strategy with the multiple difficulties problem.

Figure 601: Log-Log plot of the convergence of the

NLP strategy with the multiple difficulties problem.

Figure 602: Log-Log plot of the convergence of

the PRIOR2P strategy with the multiple difficulties problem.

Figure 603: Log-Log plot of the convergence of the

REFSOLN EDGE strategy with the multiple difficulties problem.

198
Figure 604: Log-Log plot of the convergence of the

REFSOLN ELEM strategy with the multiple difficulties problem.

Figure 605: Log-Log plot of the convergence of the

SMOOTH PRED strategy with the multiple difficulties problem.

Figure 606: Log-Log plot of the convergence of the

T3S strategy with the multiple difficulties problem.

Figure 607: Log-Log plot of the convergence of the

TYPEPARAM strategy with the multiple difficulties problem.

199
Figure 608: Log-Log plot of the convergence of all strategies with the multiple difficulties problem.

200
strategy A B C

ALTERNATE 275.97 -1.03 0.24

APRIORI 2.97x1037 -75.72 0.018

COEF DECAY 149.10 -1.15 0.22

COEF ROOT 3.14 -0.33 0.28

H&P ERREST 2.14x1014 -19.96 0.066

NEXT3P 3.98x106-7.65 0.098

NLP 1.41x1033 -68.91 0.016

PRIOR2P 1.92x103-2.69 0.15

REFSOLN EDGE 1.57 -0.073 0.46

REFSOLN ELEM 3.01 -0.076 0.45

SMOOTH PRED 3.29 -0.14 0.38

T3S 150.22 -0.84 0.24

TYPEPARAM 70.19 -0.62 0.27

Table 81: Parameters of the least squares fit for

||ehp||E = AeBNC

dof for the multiple difficulties problem.

strategy factor

REFSOLN EDGE 1.00

H&P ERREST 1.40

REFSOLN ELEM 1.43

TYPEPARAM 1.49

ALTERNATE 1.52

NEXT3P 1.53

SMOOTH PRED 1.71

COEF DECAY 1.77

PRIOR2P 1.90

APRIORI 1.98

T3S 2.05

COEF ROOT 2.09

NLP 2.40

Table 82: Factor by which N is larger than the best

strategy for the multiple difficulties problem at low

accuracy, 1.0x10−2.

strategy A B

ALTERNATE 7.15 -0.25

APRIORI 0.021 -0.062

COEF DECAY 1.32 -0.19

COEF ROOT 0.82 -0.16

H&P ERREST 0.47 -0.17

NEXT3P 0.13 -0.12

NLP 0.18 -0.089

PRIOR2P 0.37 -0.14

REFSOLN EDGE 28.18 -0.36

REFSOLN ELEM 60.29 -0.35

SMOOTH PRED 11.05 -0.26

T3S 4.61 -0.22

TYPEPARAM 7.86 -0.27

Table 83: Parameters of the least squares fit for

||ehp||E = AeBN1/3

dof for the multiple difficulties problem.

strategy factor

REFSOLN EDGE 1.00

REFSOLN ELEM 1.26

TYPEPARAM 2.07

SMOOTH PRED 2.18

ALTERNATE 2.37

T3S 3.34

H&P ERREST 4.02

COEF DECAY 4.13

COEF ROOT 6.20

NEXT3P 7.82

PRIOR2P 8.00

APRIORI 39.60

NLP 224.68

Table 84: Factor by which N is larger than the best

strategy for the multiple difficulties problem at high

accuracy, 1.0x10−6.

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5.22 Computation Time

In the previous sections we presented performance results for the hp-adaptive strategies on a number of

test problems in terms of error vs. the number of degrees of freedom. It would be interesting to also see

a comparison in terms of error vs. computation time. However, we do not believe we could perform a

fair comparison of that nature at this time for a number of reasons, not the least of which is that the

implementation of the strategies in PHAML emphasized correctness of the method and was not tuned for

optimal performance. Nevertheless, to satisfy one’s curiosity about computation time, we present timing

results for one problem, the mild peak problem at a tolerance of 10−6. These times should not be taken

too seriously; they should only be viewed as a rough estimate of the relative time required by each of the

strategies.

These computations were performed in single user mode on a single core of a Dell Latitude D630 with

the Intel Core 2 Duo processor T7700 operating under the CentOS 5.5 distribution of Linux with the 2.6.18

kernel. PHAML Version 1.8.1 was compiled with the Intel Fortran 95 compiler Version 11.1.072 using -O

for optimization.

The results are given in Table 85. The first column gives the total wall clock time (in seconds) spent

in refinement. There is some variation in the number of times each strategy went through the refine/solve

loop making it difficult to compare the time spent in a single refinement phase of the loop using only these

numbers. The second column gives the number of refine/solve loops, and the third gives the quotient of the

first two columns to obtain the average time spent in a refinement phase. These figures show pretty much

what one would expect a priori. Most of the strategies use between 0.035 and 0.111 seconds per refinement

phase, which, due to the considerations above, should be considered approximately equal in this context,

roughly .07 seconds. The H&P ERREST strategy takes about twice as long, which makes sense because it

computes two error indicators instead of one. The NEXT3P strategy takes about ten times longer, which

makes sense because, not only is it computing three error indicators, but those error indicators are more

expensive than the basic error indicator because they use a higher polynomial degree. The two reference

solution strategies are roughly equal and take much longer than most strategies because they solve the

expensive reference solution. Finally, NLP is extremely expensive, taking about 5000 times as long as the

typical strategy because it has to solve the optimization problem.

5.23 Summary and Observations

In this section, we summarize the results in Sections 5.1–5.21 to examine the relative performance of the

strategies in different situations. The test problems are grouped into six categories: easy problems, hard

problems, and singular problems at low accuracy and high accuracy. We present the comparisons in two

forms.

Tables 86–91 give a straight-forward ranking of the strategies for each problem based on the 3-parameter

least squares fit. The four best strategies for each problem are highlighted in green, and the four worst in

red to make it easy to see which strategies are consistently good or bad in a given category.

202
strategy total time number of average time

in refinement ref/solve loops per refinement

(s.) (s./loop)

ALTERNATE 1.55 16 0.097

APRIORI 0.95 27 0.035

COEF DECAY 0.94 11 0.085

COEF ROOT 0.88 12 0.073

H&P ERREST 1.44 11 0.131

NEXT3P 7.09 11 0.645

NLP 3969.16 13 305.320

PRIOR2P 1.33 12 0.111

REFSOLN EDGE 29.38 19 1.546

REFSOLN ELEM 20.01 12 1.668

SMOOTH PRED 1.03 11 0.094

T3S 0.38 8 0.048

TYPEPARAM 1.08 15 0.072

Table 85: Wall clock time for the refinement phases of the solution of the mild peak problem with τ = 10−6,

the number of refine/solve loops, and the average time for a refinement phase of the loops.

203
strategy

analyticmild peakmild boundary layermild oscillatorymild wave front

ALTERNATE 11 13 11 12 12

APRIORI 4 3 13 1 6

COEF DECAY 6 12 6 9 5

COEF ROOT 7 9 8 13 10

H&P ERREST 9 6 1 8 2

NEXT3P 2 5 4 6 4

NLP 12 7 7 10 11

PRIOR2P 8 10 5 11 7

REFSOLN EDGE 1 1 3 3 1

REFSOLN ELEM 5 2 9 2 3

SMOOTH PRED 10 11 10 7 8

T3S 13 8 12 5 13

TYPEPARAM 3 4 2 4 9

Table 86: Low accuracy ranking of each strategy for

easy problems.

strategysharp peakstrong boundary layerstrong oscillatorysteep wave frontasymmetric wave front

ALTERNATE 9 2 12 10 11

APRIORI 11 13 1 11 10

COEF DECAY 5 10 9 5 7

COEF ROOT 7 11 10 9 9

H&P ERREST 8 9 8 6 4

NEXT3P 4 4 7 4 3

NLP 12 8 13 12 13

PRIOR2P 6 12 11 7 6

REFSOLN EDGE 1 1 4 1 1

REFSOLN ELEM 2 5 5 2 2

SMOOTH PRED 13 7 6 3 5

T3S 10 3 2 13 12

TYPEPARAM 3 6 3 8 8

Table 87: Low accuracy ranking of each strategy for

hard problems.

strategyanalyticmild peakmild boundary layermild oscillatorymild wave front

ALTERNATE 12 13 12 12 13

APRIORI 1 2 13 1 8

COEF DECAY 8 12 5 8 7

COEF ROOT 6 10 8 9 9

H&P ERREST 13 8 11 13 11

NEXT3P 9 7 9 10 10

NLP 7 9 6 7 4

PRIOR2P 10 11 10 11 12

REFSOLN EDGE 4 4 2 3 2

REFSOLN ELEM 3 1 4 2 1

SMOOTH PRED 5 6 3 5 5

T3S 11 5 7 6 6

TYPEPARAM 2 3 1 4 3

Table 88: High accuracy ranking of each strategy for

easy problems.

strategysharp peakstrong boundary layerstrong oscillatorysteep wave frontasymmetric wave front

ALTERNATE 13 1 12 3 4

APRIORI 8 13 2 9 9

COEF DECAY 10 8 7 8 8

COEF ROOT 9 11 8 10 10

H&P ERREST 6 9 10 7 6

NEXT3P 7 4 9 11 11

NLP 5 12 13 13 13

PRIOR2P 11 10 11 12 12

REFSOLN EDGE 2 2 3 1 1

REFSOLN ELEM 1 3 4 2 2

SMOOTH PRED 12 5 6 6 7

T3S 4 7 1 5 5

TYPEPARAM 3 6 5 4 3

Table 89: High accuracy ranking of each strategy for

hard problems.

204
strategy

nearly straight reentrant cornerwide angle reentrant cornerL-shaped domainnarrow angle reentrant cornerslit domainmode 1 linear elasticitymode 2 linear elasticitybatterysingular wellintersecting interfacesmultiple difficulties

ALTERNATE 11 11 11 12 12 12 11 10 12 12 5

APRIORI 10 9 5 3 3 2 8 5 6 2 10

COEF DECAY 3 1 1 2 2 3 3 4 5 3 8

COEF ROOT 5 2 3 4 5 5 4 12 10 4 12

H&P ERREST 1 3 7 8 8 8 5 1 3 11 2

NEXT3P 2 5 8 9 9 6 10 3 7 9 6

NLP 4 7 4 11 11 11 9 9 13 10 13

PRIOR2P 8 6 6 6 7 9 6 6 9 6 9

REFSOLN EDGE 6 4 2 1 1 1 1 11 1 1 1

REFSOLN ELEM 9 8 9 5 6 4 7 2 8 8 3

SMOOTH PRED 12 12 12 10 10 10 12 8 4 7 7

T3S 13 13 13 13 13 13 13 7 2 13 11

TYPEPARAM 7 10 10 7 4 7 2 13 11 5 4

Table 90: Low accuracy ranking of each strategy for singular problems.

The ranking of the strategies indicates which strategies did best, but it does not indicate how much better

one strategy is than another (or how close they are to being nearly the same). For this we can examine

the factor by which N for a particular strategy is larger than N for the best strategy, as described at the

beginning of Section 5. The factors are illustrated in Figures 609–614. Each circle represents the factor for

one problem in the given category. If there is a number at the top of the graph, it indicates the number of

factors that are larger than 10. The strategies that performed the best in that category have all the circles

near the bottom of the graph, as in REFSOLN EDGE, REFSOLN ELEM and TYPEPARAM in Figure

609. To the right of the graph, the strategies are ranked according to the average of the factors for that

category.

Based on the tables and figures in this section and Section 5.22, we make the following observations.

• REFSOLN EDGE and REFSOLN ELEM are the top two strategies in all categories except singular

problems at low accuracy where they are in the top 5 with factors less than 2. Also note that REFSOLN EDGE would have been the best strategy in that category if it had not performed poorly on

the battery problem. The two strategies are equally good with each of them having the better average

factor in three categories, and the largest ratio of their average factors being about 1.35. However, these

strategies are considerably more expensive than most strategies.

• TYPEPARAM is the third best strategy in all categories of nonsingular problems, and is in the middle

of the pack for singular problems where it has an average factor of 2.26 for low accuracy and 3.27 for

205
strategy

nearly straight reentrant cornerwide angle reentrant cornerL-shaped domainnarrow angle reentrant cornerslit domainmode 1 linear elasticitymode 2 linear elasticitybatterysingular wellintersecting interfacesmultiple difficulties

ALTERNATE 13 12 12 12 12 11 12 10 9 12 5

APRIORI 1 1 1 3 2 2 2 3 6 1 12

COEF DECAY 7 7 7 7 8 8 8 7 7 3 8

COEF ROOT 4 6 6 6 7 10 6 12 10 6 9

H&P ERREST 8 9 9 10 10 7 9 1 12 11 7

NEXT3P 10 10 11 11 9 13 13 8 8 9 10

NLP 11 11 10 9 11 6 5 4 13 10 13

PRIOR2P 6 4 4 5 6 9 4 9 11 8 11

REFSOLN EDGE 3 3 2 1 1 1 1 11 1 2 1

REFSOLN ELEM 2 2 3 2 3 3 3 2 2 5 2

SMOOTH PRED 9 5 5 4 4 4 7 6 3 4 4

T3S 12 13 13 13 13 12 11 5 4 13 6

TYPEPARAM 5 8 8 8 5 5 10 13 5 7 3

Table 91: High accuracy ranking of each strategy for singular problems.

206
Figure 609: Factors by which N is larger than the best strategy for each easy problem at low accuracy. The

table contains the average over all problems in the category.

Figure 610: Factors by which N is larger than the best strategy for each easy problem at high accuracy.

The table contains the average over all problems in the category.

207
Figure 611: Factors by which N is larger than the best strategy for each hard problem at low accuracy. The

table contains the average over all problems in the category.

Figure 612: Factors by which N is larger than the best strategy for each hard problem at high accuracy.

The table contains the average over all problems in the category.

208
Figure 613: Factors by which N is larger than the best strategy for each singular problem at low accuracy.

The table contains the average over all problems in the category.

Figure 614: Factors by which N is larger than the best strategy for each singular problem at high accuracy.

The table contains the average over all problems in the category.

209
high accuracy.

• SMOOTH PRED is in the top 5 in all categories at high accuracy, and is the third best strategy for

singular problems at high accuracy. But at low accuracy its average factors are in the middle of the

pack and it is in the bottom four for many problems.

• APRIORI performs very well on singular problems with known point singularities and three of the five

easy problems at both low and high accuracy. But it performs poorly on the hard problems, except for

the strong oscillatory problem, and very poorly with the boundary layer.

• NEXT3P performs very well on nonsingular problems at low accuracy and fairly well on singular problems at low accuracy, but it is a bit more expensive than most strategies. It is below the middle of the

pack at high accuracy with average factors around 5.

• T3S performs fairly well on nonsingular problems, but very poorly on singular problems where it has

the largest average factor at both low and high accuracy, and is the worst strategy on about half of the

singular problems.

• PRIOR2P performs poorly on nonsingular problems, but did very well on singular problems at low

accuracy and fairly well on singular problems at high accuracy.

• COEF DECAY is in the middle of the pack in all categories except for singular problems at low accuracy

where it has the smallest average factor and is in the top four for most problems.

• H&P ERREST is in the middle of the pack in all categories except easy problems at high accuracy

where it performed poorly.

• COEF ROOT performed poorly on nonsingular problems and is in the middle of the pack on singular

problems.

• ALTERNATE performs very poorly in all categories, although it did well on a few of the hard problems.

• NLP performs poorly in most cases and is extremely expensive.

6 Conclusion and Future Work

In this paper we presented the results of a study of strategies for the hp-adaptive finite element method for

2D linear elliptic partial differential equations using newest node bisection of triangles. The hp-strategies are

methods for determining how to select between the different possibilities of h- and p-refinement. Thirteen

strategies were described and compared in a numerical experiment using 21 test problems. The primary

metric for comparison was the convergence of the relative energy norm of the error vs. the number of degrees

of freedom. A rough comparison of computation time was also presented, confirming the a priori expectations

of the relative expense of the strategies.

We found that the REFSOLN EDGE and REFSOLN ELEM strategies performed best overall, in convergence, and are comparable to each other. However, they are considerably more expensive than other

viable strategies. For problems with known point singularities and no other significant features, APRIORI

appears to be the less expensive method of choice. For nonsingular problems, TYPEPARAM performs very

well and is quite inexpensive. Another inexpensive strategy that performed very well at high accuracy is

SMOOTH PRED. Most of the other strategies have their good and bad moments.

210
Since the determination of what strategies to include in this study, other strategies have come to our

attention or have come into existence. For future work we will extend the results of this study to include

additional strategies as they are discovered. Also, we hope to use the lessons learned from this study to

develop a better general purpose hp-strategy. For example, is it possible to get the excellent convergence

performance of the reference solution strategies without the expense of computing the reference solution

by combining some aspects of the reference solution strategies with some aspects of other strategies? Our

conclusion is that, at this time, there is still much opportunity for the development of a general purpose

hp-adaptive strategy that is both efficient and effective.

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