prefiltering based esprit for estimating sinusoidal parameters in non gaussian arma noise addresses the esprit algorithm for estimating sinusoidal parameters in non gaussian arma noise the authors show that after prefiltering the output data via the estimated ar polynomial of the noise model a new esprit based on some extensions of esprit can be used to estimate sinusoidal parameters

generalized fictitious methods for fluid structure interactions analysis and simulations we present a new fictitious pressure method for fluid structure interaction fsi problems in incompressible flow by generalizing the fictitious mass and damping methods we published previously in 1 the fictitious pressure method involves modification of the fluid solver whereas the fictitious mass and damping methods modify the structure solver we analyze all fictitious methods for simplified problems and obtain explicit expressions for the optimal reduction factor convergence rate index at the fsi interface 2 this analysis also demonstrates an apparent similarity of fictitious methods to the fsi approach based on robin boundary conditions which have been found to be very effective in fsi problems we implement all methods including the semi implicit robin based coupling method in the context of spectral element discretization which is more sensitive to temporal instabilities than low order methods however the methods we present here are simple and general and hence applicable to fsi based on any other spatial discretization in numerical tests we verify the selection of optimal values for the fictitious parameters for simplified problems and for vortex induced vibrations viv even at zero mass ratio for ever resonance we also develop an empirical a posteriori analysis for complex geometries and apply it to 3d patient specific flexible brain arteries with aneurysms for very large deformations we demonstrate that the fictitious pressure method enhances stability and convergence and is comparable or better in most cases to the robin approach or the other fictitious methods

robust characterizations of polynomials withapplications to program testing the study of self testing and self correcting programs leads to the search for robust characterizations of functions here the authors make this notion precise and show such a characterization for polynomials from this characterization the authors get the following applications simple and efficient self testers for polynomial functions are constructed the characterizations provide results in the area of coding theory by giving extremely fast and efficient error detecting schemes for some well known codes this error detection scheme plays a crucial role in subsequent results on the hardness of approximating some np optimization problems

a robin robin preconditioner for advection diffusion equations with discontinuous coefficients abstract we consider an advection diffusion problem with discontinuous viscosity coefficients we apply a substructuring technique and we extend to the resulting schur complement the robin robin preconditioner used for problems with constant viscosity a quasi optimal convergence analysis is performed in the case of uniform convection by means of fourier techniques the variational formulation in order to generalize the preconditioner to an arbitrary number of subdomains is also addressed as well as some numerical tests in 3d

optimized schwarz methods without overlap for the helmholtz equation the classical schwarz method is a domain decomposition method to solve elliptic partial differential equations in parallel convergence is achieved through overlap of the subdomains we study in this paper a variant of the schwarz method which converges without overlap for the helmholtz equation we show that the key ingredients for such an algorithm are the transmission conditions we derive optimal transmission conditions which lead to convergence of the algorithm in a finite number of steps these conditions are however nonlocal in nature and we introduce local approximations which we optimize for performance of the schwarz method this leads to an algorithm in the class of optimized schwarz methods we present an asymptotic analysis of the optimized schwarz method for two types of transmission conditions robin conditions and transmission conditions with second order tangential derivatives numerical results illustrate the effectiveness of the optimized schwarz method on a model problem and on a problem from industry

robin robin preconditioned krylov methods for fluid structure interaction problems in this work we propose a robin robin preconditioner combined with krylov iterations for the solution of the interface system arising in fluid structure interaction fsi problems it can be seen as a partitioned fsi procedure and in this respect it generalizes the ideas introduced in s badia f nobile c vergara j comput phys 227 2008 7027 7051 we analyze the convergence of gmres iterations with the robin robin preconditioner on a model problem and compare its efficiency with some existing algorithms the method is shown to be very efficient for many challenging fluid structure interaction problems such as those characterized by a large added mass effect or by enclosed fluids in particular the possibility to solve balloon type problems without any special treatment makes this algorithm very appealing compared to the computationally intensive existing approaches c 2009 elsevier b v all rights reserved

property testing and its connection to learning and approximation in this paper we consider the question of determining whether a function f has property p or is e far from any function with property p a property testing algorithm is given a sample of the value of f on instances drawn according to some distribution in some cases it is also allowed to query f on instances of its choice we study this question for different properties and establish some connections to problems in learning theory and approximation in particular we focus our attention on testing graph properties given access to a graph g in the form of being able to query whether an edge exists or not between a pair of vertices we devise algorithms to test whether the underlying graph has properties such as being bipartite k colorable or having a p clique clique of density p with respect to the vertex set our graph property testing algorithms are probabilistic and make assertions that are correct with high probability while making a number of queries that is independent of the size of the graph moreover the property testing algorithms can be used to efficiently i e in time linear in the number of vertices construct partitions of the graph that correspond to the property being tested if it holds for the input graph

fast monte carlo algorithms for finding low rank approximations we consider the problem of approximating a given m n matrix a by another matrix of specified rank k which is smaller than m and n the singular value decomposition svd can be used to find the best such approximation however it takes time polynomial in m n which is prohibitive for some modern applications in this article we develop an algorithm that is qualitatively faster provided we may sample the entries of the matrix in accordance with a natural probability distribution in many applications such sampling can be done efficiently our main result is a randomized algorithm to find the description of a matrix d of rank at most k so that holds with probability at least 1 where v vf is the frobenius norm the algorithm takes time polynomial in k 1 e log 1 only and is independent of m and n in particular this implies that in constant time it can be determined if a given matrix of arbitrary size has a good low rank approximation

on approximating the number of k cliques in sublinear time we study the problem of approximating the number of k cliques in a graph when given query access to the graph we consider the standard query model for general graphs via 1 degree queries 2

well posedness regularity and convergence analysis of the finite element approximation of a generalized robin boundary value problem in this paper we propose the mathematical and finite element analysis of a second order partial differential equation endowed with a generalized robin boundary condition which involves the laplace beltrami operator by introducing a function space h 1 omega gamma of h 1 omega functions with h 1 gamma traces where gamma subseteq partial omega based on a variational method we prove that the solution of the generalized robin boundary value problem possesses a better regularity property on the boundary than in the case of the standard robin problem we numerically solve generalized robin problems by means of the finite element method with the aim of validating the theoretical rates of convergence of the error in the norms associated to the space h 1 omega gamma

a generalized least absolute deviation method for parameter estimation of autoregressive signals this paper proposes a generalized least absolute deviation glad method for parameter estimation of autoregressive ar signals under non gaussian noise environments the proposed glad method can improve the accuracy of the estimation of the conventional least absolute deviation lad method by minimizing a new cost function with parameter variables and noise error variables compared with second and high order statistical methods the proposed glad method can obtain robustly an optimal ar parameter estimation without requiring the measurement noise to be gaussian moreover the proposed glad method can be implemented by a cooperative neural network nn which is shown to converge globally to the optimal ar parameter estimation within a finite time simulation results show that the proposed glad method can obtain more accurate estimates than several well known estimation methods in the presence of different noise distributions

cumulant based order determination of non gaussian arma models the objective is the order determination of non gaussian and nonminimum phase autoregressive moving average arma models using higher order cumulant statistics the two methods developed assume knowledge of upper bounds on the arma orders the first method performs a linear dependence search among the columns of a higher order statistics matrix by means of the gram schmidt orthogonalization procedure in the second method the order of the ar part is found as the rank of the matrix formed by the higher order statistics sequence for numerically robust rank determination the singular value decomposition approach is adopted the argument principle and samples of the polyspectral phase are used to obtain the relative degree of the arma model from which the order of the ma part can be determined statistical analysis is included for determining the correct ma order with high probability when estimates of third order cumulants are only available simulations are used to verify the performance of the methods and compare autocorrelation with cumulant based order determination approaches

esprit estimation of signal parameters via rotational invariance techniques an approach to the general problem of signal parameter estimation is described the algorithm differs from its predecessor in that a total least squares rather than a standard least squares criterion is used although discussed in the context of direction of arrival estimation esprit can be applied to a wide variety of problems including accurate detection and estimation of sinusoids in noise it exploits an underlying rotational invariance among signal subspaces induced by an array of sensors with a translational invariance structure the technique when applicable manifests significant performance and computational advantages over previous algorithms such as mem capon s mlm and music

fluid structure interaction with large structural displacements the calculation of viscous flows inside deformable structures faces major difficulties when enforcing the kinematic compatibility at the fluid structure interface and updating the geometry of the domain this paper proposes to overcome these problems by considering the fluid and the structure as a unique continuous medium to be studied in a fixed reference configuration the resulting problem is then split into a fluid and a structural part through an additive decomposition of the space of kinematically admissible test functions this approach treats the structure in a fully lagrangian way and uses an associated arbitrary lagrangian eulerian ale formulation for the fluid such a strategy has three advantages which are detailed in the present paper it can be discretised in time by implicit stable energy conserving time integration schemes and solved by simple iterative uncoupled algorithms the fluid and the structural problems can be approximated by independent finite element spaces the most recent geometrically exact nonlinear shell models can be used for the structures the full strategy has been implemented into an industrial cfd code results obtained in the simulation of industrial hydraulic shock absorbers are presented at the end of the paper

flow rate boundary problems for an incompressible fluid in deformable domains formulations and solution methods in this paper we consider the numerical solution of the interaction of an incompressible fluid and an elastic structure in a truncated computational domain as well known in this case there is the problem of prescribing realistic boundary data on the artificial sections when only partial data are available this problem has been investigated extensively for the rigid case in this work we start considering the compliant case by focusing on the flow rate conditions for the fluid we propose three formulations of this problem different algorithms for its numerical solution and carry out several 2d numerical simulations with the aim of comparing the performances of the different algorithms

a minimum spanning tree algorithm with inverse ackermann type complexity a deterministic algorithm for computing a minimum spanning tree of a connected graph is presented its running time is 0 m m n where is the classical functional inverse of ackermann s function and n respectively m is the number of vertices respectively edges the algorithm is comparison based it uses pointers not arrays and it makes no numeric assumptions on the edge costs

approximating the minimum spanning tree weight in sublinear time we present a probabilistic algorithm that given a connected graph g represented by adjacency lists of average degree d with edge weights in the set 1 w and given a parameter 0 eps 1 2 estimates in time o dw varepsilon 2 log frac dw varepsilon the weight of the minimum spanning tree mst of g with a relative error of at most eps note that the running time does not depend on the number of vertices in g we also prove a nearly matching lower bound of omega dw varepsilon 2 on the probe and time complexity of any approximation algorithm for mst weight the essential component of our algorithm is a procedure for estimating in time o d eps 2 log frac d varepsilon the number of connected components of an unweighted graph to within an additive error of varepsilon n this becomes o eps 2 log frac 1 varepsilon for d o 1 the time bound is shown to be tight up to within the log frac d varepsilon factor our connected components algorithm picks o 1 varepsilon 2 vertices in the graph and then grows local spanning trees whose sizes are specified by a stochastic process from the local information collected in this way the algorithm is able to infer with high confidence an estimate of the number of connected components we then show how estimates on the number of components in various subgraphs of g can be used to estimate the weight of its mst

esprit a subspace rotation approach to estimation of parameters of cisoids in noise the application of a subspace invariance approach esprit to the estimation of parameters frequencies and powers of cisoids in noise is described esprit exploits an underlying rotational invariance of signal subspaces spanned by two temporally displaced data sets the new approach has several advantages including improved resolution over pisarenko s technique for harmonic retrieval

an effective fluid structure interaction formulation for vascular dynamics by generalized robin conditions in this work we focus on the modeling and numerical simulation of the fluid structure interaction mechanism in vascular dynamics we first propose a simple membrane model to describe the deformation of the arterial wall which is derived from the koiter shell equations and is applicable to an arbitrary geometry secondly we consider a reformulation of the fluid structure problem in which the newly derived membrane model thanks to its simplicity is embedded into the fluid equations and will appear as a generalized robin boundary condition the original problem is then reduced to the solution of subsequent fluid equations defined on a moving domain and may be achieved with a fluid solver only we also derive a stability estimate for the resulting numerical scheme finally we propose new outflow absorbing boundary conditions which are easy to implement and allow us to reduce significantly the spurious pressure wave reflections that typically appear in artificially truncated computational domains we present several numerical results showing the effectiveness of the proposed approaches

inexact accurate partitioned algorithms for fluid structure interaction problems with finite elasticity in haemodynamics in this paper we consider the numerical solution of the three dimensional fluid structure interaction problem in haemodynamics in the case of real geometries physiological data and finite elasticity vessel deformations we study some new inexact schemes obtained from semi implicit approximations which treat exactly the physical interface conditions while performing just one or few iterations for the management of the interface position and of the fluid and structure non linearities we show that such schemes allow to improve the efficiency while preserving the accuracy of the related exact implicit scheme to do this we consider both a simple analytical test case and two real cases of clinical interest in haemodynamics we also provide an error analysis for a simple differential model problem when a bdf method is considered for the time discretization and only few newton iterations are performed at each temporal instant

analysis and optimization of the generalized schwarz method for elliptic problems with application to fluid structure interaction we propose a unified convergence analysis of the generalized schwarz method applied to a linear elliptic problem for a general interface flat cylindrical or spherical in any dimension in particular we provide the exact convergence set of the interface symbols related to the operators involved in the transmission conditions we also provide a general procedure to obtain estimates of the optimized interface symbols within the constants we apply such general results to a simple fluid structure interaction model problem given by the interaction between an incompressible inviscid fluid and the wave equation finally we assess the effectiveness of the theoretical findings through three dimensional numerical experiments in the haemodynamic context obtained by solving the coupling between the navier stokes equations and the linear infinitesimal elasticity

the complexity of colouring problems on dense graphs abstract we consider the problem of deciding whether or not a graph has a vertex k colouring restricted to the class of graphs in which each vertex has degree at least n where is a fixed positive constant and n is the number of vertices of the graph we show that there is a deterministic polynomial time algorithm for this problem when k 3 k 2 and that this is best possible we also consider the corresponding enumeration problems

on svd for estimating generalized eigenvalues of singular matrix pencil in noise several algorithms for estimating generalized eigenvalues ges of singular matrix pencils perturbed by noise are reviewed the singular value decomposition svd is explored as the common structure in the three basic algorithms direct matrix pencil algorithm pro esprit and tls esprit it is shown that several svd based steps inherent in the algorithms are equivalent to the first order approximation in particular the pro esprit and its variant tls pro esprit are shown to be equivalent and the tls esprit and its earlier version ls esprit are shown to be asymptotically equivalent to the first order approximation for the problem of estimating superimposed complex exponential signals the state space algorithm is shown to be also equivalent to the previous matrix pencil algorithms to the first order approximation the second order perturbation and the threshold phenomenon are illustrated by simulation results based on a damped sinusoidal signal an improved state space algorithm is found to be the most robust to noise

fluid structure partitioned procedures based on robin transmission conditions in this article we design new partitioned procedures for fluid structure interaction problems based on robin type transmission conditions the choice of the coefficient in the robin conditions is justified via simplified models the strategy is effective whenever an incompressible fluid interacts with a relatively thin membrane as in hemodynamics applications we analyze theoretically the new iterative procedures on a model problem which represents a simplified blood vessel system in particular the robin neumann scheme exhibits enhanced convergence properties with respect to the existing partitioned procedures the theoretical results are checked using numerical experimentation

sublinear time algorithms for monomer dimer systems on bounded degree graphs for a graph g let z g be the partition function of the monomer dimer system defined by k m k g k where m k g is the number of matchings of size k in g we consider graphs of bounded degree and develop a sublinear time algorithm for estimating logz g at an arbitrary value 0 within additive error en with high probability the query complexity of our algorithm does not depend on the size of g and is polynomial in 1 e and we also provide a lower bound quadratic in 1 e for this problem this is the first analysis of a sublinear time approximation algorithm for a p complete problem our approach is based on the correlation decay of the gibbs distribution associated with z g we show that our algorithm approximates the probability for a vertex to be covered by a matching sampled according to this gibbs distribution in a near optimal sublinear time we extend our results to approximate the average size and the entropy of such a matching within an additive error with high probability where again the query complexity is polynomial in 1 e and the lower bound is quadratic in 1 e our algorithms are simple to implement and of practical use when dealing with massive datasets our results extend to other systems where the correlation decay is known to hold as for the independent set problem up to the critical activity

modular vs non modular preconditioners for fluid structure systems with large added mass effect in this article we address the numerical simulation of fluid structure interaction fsi problems featuring large added mass effect we analyze different preconditioners for the coupled system matrix obtained after space time discretization and linearization of the fsi problem the classical dirichlet neumann preconditioner has the advantage of modularity because it allows to reuse existing fluid and structure codes with minimum effort simple interface communication unfortunately its performance is very poor in case of large added mass effects alternatively we consider two non modular approaches the first one consists in preconditioning the coupled system with a suitable diagonal scaling combined with an ilut preconditioner the system is then solved by a krylov method the drawback of this procedure is that the combination of fluid and structure codes to solve the coupled system is not straightforward the second non modular approach we consider is a splitting technique based on an inexact block lu factorization of the linear fsi system the resulting algorithm computes the fluid velocity separately from the coupled pressure structure system at each iteration reducing the computational cost independently of the preconditioner the efficiency of semi implicit algorithms i e those that treat geometric and fluid nonlinearities in an explicit way is highlighted and their performance compared to the one of implicit algorithms all the methods are tested on three dimensional blood vessel systems the algorithm combining the non modular ilut preconditioner with krylov methods proved to be the fastest

small bias probability spaces efficient constructions and applications it is shown how to efficiently construct a small probability space on n binary random variables such that for every subset its parity is either zero or one with almost equal probability they are called epsilon biased random variables the number of random bits needed to generate the random variables is o log n log frac 1 epsilon thus if epsilon is polynomially small then the size of the sample space is also polynomial random variables that are epsilon biased can be used to construct almost k wise independent random variables where epsilon is a function of k these probability spaces have various applications l derandomization of algorithms many randomized algorithms that require only k wise independence of their random bits where k is bounded by o log n can be derandomized by using epsilon biased random variables 2 reducing the number of random bits required by certain randomized algorithms e g verification of matrix multiplication 3 exhaustive tes

generalizations and accelerations of lions nonoverlapping domain decomposition method for linear elliptic pde in this paper a one parameter generalization of lions nonoverlapping domain decomposition method for linear elliptic pdes is proposed and studied the generalized methods are shown to be descent direction methods for minimizing an interface bias functional iteration convergence of both the continuous and finite element versions of the proposed methods is established it is theoretically and numerically demonstrated that for generic choices of the parameter the generalized methods converge faster than lions original method algorithms are given and numerical results are presented

harmonic retrieval in colored non gaussian noise using cumulants this paper addresses the harmonic retrieval problem in colored linear non gaussian noise of unknown covariance and unknown distribution the assumptions made in the reported studies that the non gaussian noise is asymmetrically distributed and no quadratic phase coupling occurs are released using the elaborately defined fourth order cumulants of the complex noisy observations which are obtained by hilbert transform we can estimate either the correlation or the ar polynomial of the non gaussian noise via cumulant projections or arma modeling then the prewhitening or prefiltering techniques can be employed to retrieve harmonics respectively simulation results are presented to demonstrate the effectiveness of the proposed algorithms

analysis and optimization of robin robin partitioned procedures in fluid structure interaction problems in the solution of fluid structure interaction fsi problems partitioned procedures are modular algorithms that involve separate fluid and structure solvers that interact in an iterative framework through the exchange of suitable transmission conditions at the fs interface in this work we study using fourier analysis the convergence of partitioned algorithms based on robin transmission conditions we derive for different models of the fluid and the structure a frequency dependent reduction factor at each iteration of the partitioned algorithm which is minimized by choosing optimal values of the coefficients in the robin transmission conditions two dimensional numerical results are also reported which highlight the effectiveness of the optimization procedure

fluid structure algorithms based on steklov poincare operators in this paper we review some classical algorithms for fluid structure interaction problems and we propose an alternative viewpoint mutuated from the domain decomposition theory this approach yields preconditioned richardson iterations on the steklov poincare nonlinear equation at the fluid structure interface

cumulant based approach to harmonic retrieval and related problems a frequently encountered problem in signal processing is that of estimating the frequencies and amplitudes of harmonics observed in additive colored gaussian noise in practice the observed signals are contaminated with spatially and temporally colored noise of unknown power spectral density a cumulant based approach to these problems is proposed the cumulants of complex processes are defined and it is shown that specific 1 d slices of the fourth order cumulant of the noisy signal for the direction of arrival doa and retrieval of harmonics in noise rhn problems are identical to the autocorrelation of a related noiseless signal hence correlation based high resolution methods may be used with fourth order cumulants as well the effectiveness of the proposed methods is demonstrated through standard simulation examples

approximating the minimum vertex cover in sublinear time and a connection to distributed algorithms for a given graph g over n vertices let opt g denote the size of an optimal solution in g of a particular minimization problem e g the size of a minimum vertex cover a randomized algorithm will be called an a approximation algorithm with an additive error for this minimization problem if for any given additive error parameter e 0 it computes a value opt such that with probability at least 2 3 it holds that opt g opt a opt g en assume that the maximum degree or average degree of g is bounded in this case we show a reduction from local distributed approximation algorithms for the vertex cover problem to sublinear approximation algorithms for this problem this reduction can be modified easily and applied to other optimization problems that have local distributed approximation algorithms such as the dominating set problem we also show that for the minimum vertex cover problem the query complexity of such approximation algorithms must grow at least linearly with the average degree d of the graph this lower bound holds for every multiplicative factor a and small constant e as long as d o n a in particular this means that for dense graphs it is not possible to design an algorithm whose complexity is o n

splitting methods based on algebraic factorization for fluid structure interaction we discuss in this paper the numerical approximation of fluid structure interaction fsi problems dealing with strong added mass effect we propose new semi implicit algorithms based on inexact block lu factorization of the linear system obtained after the space time discretization and linearization of the fsi problem as a result the fluid velocity is computed separately from the coupled pressure structure velocity system at each iteration reducing the computational cost we investigate explicit implicit decomposition through algebraic splitting techniques originally designed for the fsi problem this approach leads to two different families of methods which extend to fsi the algebraic pressure correction method and the yosida method two schemes that were previously adopted for pure fluid problems furthermore we have considered the inexact factorization of the fluid structure system as a preconditioner the numerical properties of these methods have been tested on a model problem representing a blood vessel system

optimized schwarz methods for the diffusion reaction problem with cylindrical interfaces in this work we consider the optimized schwarz method for the three dimensional 3d diffusion reaction problem in particular we treat the case of cylindrical interfaces between the subdomains and we provide a convergence analysis of the schwarz method both in the case of dirichlet interface conditions and in that of general transmission conditions this allows us to recover for the latter case optimal symbols for the interface conditions which are supposed to work well for geometries which feature cylindrical interfaces moreover starting from these optimal symbols we propose effective and easily computable constant interface parameters derived both from taylor expansions and from an optimization procedure we finally present several 3d numerical results aiming at validating the theoretical findings

artificial added mass instabilities in sequential staggered coupling of nonlinear structures and incompressible viscous flows this note investigates the so called arti cial added mass e ect which is responsible for devastating instabilities within sequentially staggered fluid structure interaction fsi simulations where incompressible fluids are considered a discrete representation of the added mass operatorma is given and instability conditions are evaluated for different temporal discretisation schemes it is proven that for every sequentially staggered scheme and given spatial discretisation of a problem a mass ratio between fluid and structural mass density can be found at which the coupled system becomes unstable the analysis is quite general and does not depend upon the particular spatial discretisation schemes used however here special attention is put on stabilised finite elements employed on the fluid partition numerical investigations further highlight the results

optimized schwarz methods optimized schwarz methods are a new class of schwarz methods with greatly enhanced convergence properties they converge uniformly faster than classical schwarz methods and their convergence rates dare asymptotically much better than the convergence rates of classical schwarz methods if the overlap is of the order of the mesh parameter which is often the case in practical applications they achieve this performance by using new transmission conditions between subdomains which greatly enhance the information exchange between subdomains and are motivated by the physics of the underlying problem we analyze in this paper these new methods for symmetric positive definite problems and show their relation to other modern domain decomposition methods like the new finite element tearing and interconnect feti variants

multiple invariance esprit a subspace fitting formulation of the esprit problem is presented that provides a framework for extending the algorithm to exploit arrays with multiple invariances in particular a multiple invariance mi esprit algorithm is developed and the asymptotic distribution of the estimates is obtained simulations are conducted to verify the analysis and to compare the performance of mi esprit with that of several other approaches the excellent quality of the mi esprit estimates is explained by recent results which state that under certain conditions subspace fitting methods of this type are asymptotically efficient

a polynomial approximation scheme for scheduling on uniform processors using the dual approximation approach in this paper we present a polynomial approximation scheme for the minimum makespan problem on uniform parallel processors more specifically the problem is to find a schedule for a set of independent jobs on a collection of machines of different speeds so that the last job to finish is completed as quickly as possible we give a family of polynomial time algorithms a such that a delivers a solution that is within a relative error of e of the optimum the technique employed is the dual approximation approach where infeasible but superoptimal solutions for a related dual problem are converted to the desired feasible but possibly suboptimal solution

new nonoverlapping domain decomposition methods for the harmonic maxwell system we study a nonoverlapping domain decomposition method for the harmonic maxwell equations with a new kind of interface condition using fourier analysis we derive suitable families of transmission conditions in r3 that involve second order tangential differential operators and that guarantee convergence for both propagative and evanescent modes such families depend upon parameters that are chosen to optimize the convergence rate of the corresponding iterative algorithm we then propose iterative solvers for the maxwell equations based on a domain decomposition procedure where such conditions are enforced on the interface some numerical results for a two domain decomposition show the effectiveness of the optimized interface conditions

a hybrid approach to harmonic retrieval in non gaussian arma noise addresses the harmonic retrieval problem in colored noise as contrasted to the reported studies in which gaussian noise was assumed this paper focuses on additive non gaussian arma noise our approach is hybrid in the sense that third order cumulants are first used to identify the ar part of the non gaussian noise process and then correlation based high resolution methods are used for the filtered process to estimate the number of harmonics and their frequencies simulation examples are presented to demonstrate the high resolution of this approach

a projection semi implicit scheme for the coupling of an elastic structure with an incompressible fluid we address the numerical simulation of fluid structure systems involving an incompressible viscous fluid this issue is particularly difficult to face when the fluid added mass acting on the structure is strong as it happens in hemodynamics for example indeed several works have shown that in such situations implicit coupling seems to be necessary in order to avoid numerical instabilities although significant improvements have been achieved during the last years solving implicit coupling often exhibits a prohibitive computational cost in this work we introduce a semi implicit coupling scheme which remains stable for a reasonable range of the discretization parameters the first idea consists in treating implicitly the added mass effect whereas the other contributions geometrical non linearities viscous and convective effects are treated explicitly the second idea relies on the fact that this kind of explicit implicit splitting can be naturally performed using a chorin temam projection scheme in the fluid we prove conditional stability of the scheme for a fully discrete formulation several numerical experiments point out the efficiency of the present scheme compared to several implicit approaches

comparisons between reduced order models and full 3d models for fluid structure interaction problems in haemodynamics when modelling the cardiovascular system the effect of the vessel wall on the blood flow has great relevance arterial vessels are complex living tissues and three dimensional specific models have been proposed to represent their behaviour the numerical simulation of the 3d 3d fluid structure interaction fsi coupled problem has high computational costs in terms of required time and memory storage even if many possible solutions have been explored to speed up the resolution of such problem we are far from having a 3d 3d fsi model that can be solved quickly in 3d 3d fsi models two of the main sources of complexity are represented by the domain motion and the coupling between the fluid and the structural part nevertheless in many cases we are interested in the blood flow dynamics in compliant vessels whereas the displacement of the domain is small and the structure dynamics is less relevant in these situations techniques to reduce the complexity of the problem can be used one consists in using transpiration conditions for the fluid model as surrogate for the wall displacement thus allowing problem s solution on a fixed domain another strategy consists in modelling the arterial wall as a thin membrane under specific assumptions figueroa et al 2006 nobile and vergara 2008 instead of using a more realistic but more computationally intensive 3d elastodynamic model using this strategy the dynamics of the vessel motion is embedded in the equation for the blood flow combining the transpiration conditions with the membrane model assumption we obtain an attractive formulation in fact instead of solving two different models on two moving physical domains we solve only a navier stokes system in a fixed fluid domain where the structure model is integrated as a generalized robin condition in this paper we present a general formulation in the boundary conditions which is independent of the time discretization scheme choice and on the stress strain constitutive relation adopted for the vessel wall structure our aim is first to write a formulation of a reduced order model with zero order transpiration conditions for a generic time discretization scheme then to compare a 3d 3d fsi model and a reduced fsi one in two realistic patient specific cases a femoropopliteal bypass and an aorta in particular we are interested in comparing the wall shear stresses in fact this quantity can be used as a risk factor for some pathologies such as atherosclerosis or thrombogenesis more in general we want to assess the accuracy and the computational convenience to use simpler formulations based on reduced order models in particular we show that in the case of small displacements using a 3d 3d fsi linear elastic model or the correspondent reduced order one yields many similar results

singular value decomposition based ma order determination of non gaussian arma models singular value decomposition svd based moving average ma order determination of non gaussian processes using higher order statistics is addressed it is shown that the ma order determination of autoregressive moving average arma models is equivalent to the rank determination of a certain error matrix and a svd approach is proposed its simplified form is applied to pure ma models to improve the robustness of the order selection a combination of the svd and the product of diagonal entries pode test is proposed some interesting applications of the two svd approaches are presented and simulations verify their performance

timely communicaton an analysis for a nonoverlapping domain decomposition iterative procedure an iterative procedure for nonoverlapping domain decomposition methods ddm is developed and analyzed which can be parallelly implemented with local communications it uses a robin boundary condition as its transmission condition on the interfaces the update of robin data of its transmission condition is a very simple relaxation between the preceding robin data and function value it need not find any derivatives at each iterative step this method can be easily applied to the discretization problems moreover it is shown that it is indeed a variant of the lions nonoverlapping ddm for the continuous problems also it can be regarded as a generalization of tang s generalized schwarz alternating method gsam in the nonoverlapping ddm

short note on the similarity between dirichlet neumann with interface artificial compressibility and robin neumann schemes for the solution of fluid structure interaction problems in this note the similarity between two implicit partitioned solution techniques for fluidstructure interaction fsi problems is analyzed using finite volume discretization of the flow equations fluid structure interaction refers to the mutual interaction between a fluid flow and a flexible structure partitioned solution techniques solve the flow equations and the structural equations separately these techniques are classified as implicit or strongly coupled if they satisfy the interaction conditions on the fluid structure interface in each time step and as explicit or loosely coupled if they do not both techniques analyzed in this note use block gauss seidel gs iterations meaning that the flow equations and the structural equations are solved consecutively within a time step until some convergence tolerance is reached as the flow and structural equations are solved separately the interaction conditions on the fluid structure interface have to be converted into boundary conditions on the common boundary of the fluid and structure subdomains several types of boundary conditions can be applied resulting in different decompositions in the case of dirichlet neumann dn decomposition the flow equations are solved with a dirichlet boundary condition given velocity on the fluid structure interface while the structural equations are solved with a neumann boundary condition given stress on the interface conversely robinneumann rn decomposition introduced in 1 denotes a robin boundary condition on the fluid side of the interface and a neumann boundary condition on the structure side the first technique in this comparison is block gauss seidel iterations applied to the monolithic system previously multiplied by a suitable permutation matrix leading to a robin neumann decomposition gs rn this first technique includes a simplified version of the structural model in the flow equations by means of a robin boundary condition to accelerate the convergence of the gs iterations 1 2 the second technique is block gauss seidel iterations with dirichletneumann decomposition and interface artificial compressibility gs dn iac this second

a randomized linear time algorithm to find minimum spanning trees we present a randomized linear time algorithm to find a minimum spanning tree in a connected graph with edge weights the algorithm uses random sampling in combination with a recently discovered linear time algorithm for verifying a minimum spanning tree our computational model is a unit cost random access machine with the restriction that the only operations allowed on edge weights are binary comparisons

an analysis of a new stable partitioned algorithm for fsi problems part i incompressible flow and elastic solids stable partitioned algorithms for fluid structure interaction fsi problems are developed and analyzed in this two part paper part i describes an algorithm for incompressible flow coupled with compressible elastic solids while part ii discusses an algorithm for incompressible flow coupled with structural shells importantly these new added mass partitioned amp schemes are stable and retain full accuracy with no sub iterations per time step even in the presence of strong added mass effects e g for light solids the numerical approach described here for bulk compressible solids extends the scheme of banks et al 1 2 for inviscid compressible flow and uses robin mixed boundary conditions with the fluid and solid solvers at the interface the basic amp robin conditions involving a linear combination of velocity and stress are determined from the outgoing solid characteristic relation normal to the fluid solid interface combined with the matching conditions on the velocity and traction two alternative forms of the amp conditions are then derived depending on whether the fluid equations are advanced with a fractional step method or not the stability and accuracy of the amp algorithm is evaluated for linearized fsi model problems the full nonlinear case being left for future consideration a normal mode analysis is performed to show that the new amp algorithm is stable for any ratio of the solid and fluid densities including the case of very light solids when added mass effects are large in contrast it is shown that a traditional partitioned algorithm involving a dirichlet neumann coupling for the same fsi problem is formally unconditionally unstable for any ratio of densities exact traveling wave solutions are derived for the fsi model problems and these solutions are used to verify the stability and accuracy of the corresponding numerical results obtained from the amp algorithm for the cases of light medium and heavy solids