a direct branching algorithm for checking the equivalence of two deterministic pushdown transducers one of which is real time strict abstract a new direct branching algorithm is presented for checking the equivalence of deterministic pushdown transducers one of whose associated deterministic pushdown automata dpdas is real time strict it is a straightforward extension of the corresponding algorithm for dpdas tomita 1982 and then proves the general applicability of our approach

solution procedures for j3 plasticity and viscoplasticity abstract a solution strategy for plasticity and viscoplasticity models with isotropic yield surfaces depending upon all the principal invariants of the stress tensor is presented basically it requires the inversion of a fourth order positive definite tensor g both for the solution of the constitutive problem and for the evaluation of the consistent tangent operator it is proved that the assumption of isotropic elastic behaviour and the isotropy of the yield criterion entail an explicit representation formula for g 1 as linear combination of dyadic and square tensor products further an analogous representation formula for the consistent tangent operator is provided by exploiting basic composition rules between dyadic and square tensor products along with rivlin s identities for tensor polynomials all tensor operations required to compute the coefficients of the adopted representation formula for g 1 are carried out in intrinsic form it is thus shown that the relevant computational burden essentially amounts to solving a linear system of order three the performances of the proposed approach are illustrated by means of some numerical examples referred to the argyris failure criterion

an extended direct branching algorithm for checking equivalence of deterministic pushdown automata abstract this paper extends the direct branching algorithm of 25 for checking equivalence of deterministic pushdown automata it does so by providing a technique called halting for dealing with nodes with unbounded degree in the comparison tree this may occur when a skipping step may be applied infinitely many times to a certain node as a result of infinite sequences of e moves this extension allows the algorithm to check equivalence of two deterministic pushdown automata when none of them is real time but in a certain condition that properly contains a case where one of them is real time strict

church rosser controlled rewriting systems and equivalence problems for deterministic context free languages we use a description of deterministic context free languages dcfl by a special type of church rosser rewriting systems to extend several procedures testing the equality of two languages in a subfamilyfof dcfl to procedures testing the equality of two languages one of which is inf the other beeing a general dcfl

a general approach to the evaluation of consistent tangent operators for rate independent elastoplasticity abstract we present a general approach to the derivation of the explicit expression of tangent operators consistent with the finite step integration schemes of the flow rule for rate independent elastoplastic models with mixed hardening by exploiting the model of generalized standard material we show that the algorithmic tangent operator can be obtained by inverting a suitable positive definite matrix use of the sherman morrison woodbury formula allows us to reduce to a half the burden associated with such inversion and to derive an expression of the consistent tangent operator prone to computer implementation the application of the proposed approach to the von mises yield criterion with linear kinematic and isotropic hardening shows that the closed form expression of the operator can be obtained by a straightforward procedure

two multiplicity free permutation representations of the general linear groupgl n q 2 soit q une puissance d un nombre premier p et soit g gl n q 2 le groupe lineaire general de degre n sur gf q 2 soit u u n q le groupe unitaire de degre n sur gf q 2 et m gl n q le groupe lineaire general sur gf q on etudie les caracteres des representations permutation de g sur les co ensembles de a la fois u et m

asai l functions and jacquet s conjecture we give a conceptually simple proof of the square integrable case of a conjecture of jacquet concerning distinguished representations of the general linear group over a local field of characteristic zero the proof is based on consideration of the rankin selberg integral representation of the generalized asai l function and utilizes global methods

on the implementation of inelastic constitutive equations with special reference to large deformation problems abstract methods for finite element analysis of inelastic problems are reviewed problems with currently popular methods based on rate principles of virtual work are pointed out a formulation is presented based on the exact incremental virtual work equation the procedure for integration of the constitutive rate equations to obtain incremental constitutive equations is based on the assumption of a constant strain rate or straight strain path during the increment full newton raphson iteration is used to solve the resulting set of nonlinear equations the treatment of the constitutive equations in this newton raphson scheme leads to a linearized form which is substantially different from the classical rate equations the procedure is implemented in a finite element program and its effectiveness is shown in a number of examples

a direct branching algorithm for checking equivalence of some classes of deterministic pushdown automata a new direct algorithm is presented for checking equivalence of some classes of deterministic pushdown automata dpda s after korenjak and hopcroft s branching algorithm it is not only powerful enough to be applicable to two dpda s accepting by empty stack one of which is real time but also simple even for dpda s in lower subclasses this is the first time the branching algorithm has been used to give such a general decision procedure without ever mixing the two languages in question in other words it deals with only the equivalence equation whose left hand side consists of a pure reachable configuration of one dpda and whose right hand side that of the other

a new fixed point algorithm for hardening plasticity based on non linear mixed variational inequalities moving from the seminal papers of han and reddy we propose a fixed point algorithm for the solution of hardening plasticity two dimensional problems the continuous problem may be classified as a mixed non linear non differentiable variational inequality of the second type and is discretized by means of a truly mixed finite element scheme one of the main peculiarities of our approach is the use of the composite triangular element of johnson and mercier for the approximation of the stress field the non differentiability is coped with via regularization whereas the non linearity is approached with a fixed point iterative strategy numerical results are proposed that investigate the sensitivity of the approach with respect to the mesh size and the regularization parameter e the simplicity of the proposed fixed point scheme with respect to more classical return mapping approaches seems to represent one of the key features of our algorithm copyright 2003 john wiley sons ltd

a polynomial time algorithm for deciding the equivalence problem for 2 tape deterministic finite state acceptors the equivalence problem for the class of one way deterministic 2 tape finite state acceptors is the problem of deciding l m 1 l m 2 where m 1 and m 2 are machines in this class a new algorithm for deciding equivalence is provided having time complexity proportional to p n where p is a polynomial and n is the size of the machines this improves upon the best previously known upper bound having order 2 cn 6 where c is a constant c beeri theoret comput sci 3 1976 pp 305 320

non smooth multisurface plasticity and viscoplasticity loading unloading conditions and numerical algorithms rate independent plasticity and viscoplasticity in which the boundary of the elastic domain is defined by an arbitrary number of yield surfaces intersecting in a non smooth fashion are considered in detail it is shown that the standard kuhn tucker optimality conditions lead to the only computationally useful characterization of plastic loading on the computational side an unconditionally convergent return mapping algorithm is developed which places no restrictions aside from convexity on the functional forms of the yield condition flow rule and hardening law the proposed general purpose procedure is amenable to exact linearization leading to a closed form expression of the so called consistent algorithmic tangent moduli for viscoplasticity a closed form algorithm is developed based on the rate independent solution the methodology is applied to structural elements in which the elastic domain possesses a non smooth boundary numerical simulations are presented that illustrate the excellent performance of the algorithm

l a l b decidability results from complete formal systems abstract the equivalence problem for deterministic pushdown automata is shown to be decidable we exhibit a complete formal system for deducing equivalent pairs of deterministic rational boolean series on the alphabet associated with a dpda m we then extend the result to deterministic pushdown transducers from a free monoid into an abelian group a general algebraic and logical framework inspired by harrison et al theoret comput sci 9 1979 173 205 conrcelle theoret comput sci 6 1978 255 279 and meitus kybernetika 5 1989 14 25 in russian is developed

consistent tangent operators for rate independent elastoplasticity abstract it is shown that for problems involving rate constitutive equations such as rate independent elastoplasticity the notion of consistency between the tangent stiffness operator and the integration algorithm employed in the solution of the incremental problem plays a crucial role in preserving the quadratic rate of asymptotic convergence of iterative solution schemes based upon newton s method within the framework of closest point projection algorithms a methodology is presented whereby tangent operators consistent with this class of algorithms may be systematically developed to wit associative j 2 flow rules with general nonlinear kinematic and isotropic hardening rules as well as a class of non associative flow rules are considered the resulting iterative solution scheme preserves the asymptotic quadratic convergence characteristic of newton s method whereas use of the socalled elastoplastic tangent in conjunction with a radial return integration algorithm a procedure often employed results in newton type of algorithms with suboptimal rate of convergence application is made to a set of numerical examples which include saturation hardening laws of exponential type

a direct branching algorithm for checking equivalence of strict deterministic vs ll k grammars abstract we present here an equivalence checking algorithm which operates directly on a pair of strict deterministic vs ll k grammars it is also straightforwardly applicable to a pair of ll k grammars though an ll k grammar is not necessarily strict deterministic the basic idea is from korenjak and hopcroft s branching algorithm for simple deterministic grammars but ours is so distinguished that it is throughout free from mixing the nonterminals of the respective grammars in question and then very simple

implicit integration procedure for viscoplastic gurson materials abstract constitutive relations and numerical integration algorithms for elastic viscoplastic ductile materials are investigated the gurson yield function is considered together with a coalescence criterion from thomason the constitutive equations are reformulated using the assumption of constant strain rate within an increment a consistency condition is incorporated into the traditional viscoplastic rate format and the tangential material operator expression is derived the algorithm is used to investigate the influence of triaxiality in the critical coalescence values of porosity

distinguished representations shintani base change and a finite field analogue of a conjecture of prasad abstract let e f be a quadratic extension of fields and g a connected quasi split reductive group over f let g o p be the opposition group obtained by twisting g by the duality involution considered by prasad assume that the field f is finite let be an irreducible generic representation of g e when is a shintani base change lift of some representation of g o p f we give an explicit nonzero g f invariant vector in terms of the whittaker vector of this shows particularly that is g f distinguished when the field f is p adic the paper also proves that the duality involution takes an irreducible admissible generic representation of g f to its contragredient as a special case of this result all generic representations of g 2 f 4 or e 8 are self dual

some decision problems about controlled rewriting systems abstract a description of deterministic context free languages by some kind of finitely generated right congruences the sets of relations generating such right congruences are called controlled rewriting systems or c systems has been given previously in the first part of this paper we study several decision problems on c systems namely the confluence problem the equivalence problem the refinement problem the class equivalence problem and the class inclusion problem in the second part of the paper we deduce from the main theorem given previously a characterisation of dcfls by means of finitely generated congruences the sets of relations generating such congruences are now ordinary finite semi thue systems we study three decision problems on finite semi thue systems namely the class equivalence problem the word problem for the syntactic congruence of one class and the partial confluence problem all the problems are investigated in several classes of c systems or semi thue systems for every class we give an answer which may be yes the problem is decidable no the problem is undecidable or eq which means that the problem is recursively equivalent to the equivalence problem for dpda

test vectors for finite periods and base change abstract let e f be a quadratic extension of finite fields by a result of gow an irreducible representation of g gl n e has at most one non zero h invariant vector up to multiplication by scalars when h is gl n f or u n e f if does have an h invariant vector it is said to be h distinguished it is known from the work of gow that h distinction is characterized by base change from u n e f due to kawanaka when h is gl n f resp from gl n f due to shintani when h is u n e f assuming is generic and h distinguished we give an explicit description of the h invariant vector in terms of the bessel function of let be a non degenerate character of n g n h and let b be the normalized bessel function of on the whittaker model for the h average w 1 h h h h b of the bessel function we prove that w i n dim dim gl n e gl n f u n e f where is the irreducible representation of u n e f resp gl n f that base changes to when h is gl n f resp u n e f as an application we classify the members of a generic l packet of sl n e that admit invariant vectors for sl n f finally we prove a p adic analogue of our result for square integrable representations in terms of formal degrees by employing the formal degree conjecture of hiraga ichino ikeda 19

a return map algorithm for general isotropic elasto visco plastic materials in principal space we describe a methodology for solving the constitutive problem and evaluating the consistent tangent operator for isotropic elasto visco plastic models whose yield function incorporates the third stress invariant the developments presented are based upon original results proved in the paper concerning the derivatives of eigenvalues and eigenprojectors of symmetric second order tensors with respect to the tensor itself and upon an original algebra of fourth order tensors obtained as second derivatives of isotropic scalar functions of a symmetric tensor argument the analysis initially referred to the small strain case is then extended to a formulation for the large deformation regime for both cases we provide a derivation of the consistent tangent tensor which shows the analogy between the two formulations and the close relationship with the tangent tensors of the lagrangian description of large strain elastoplasticity copyright 2004 john wiley sons ltd

numerical simulation of finite strain viscoplastic problems a large strain elastoplastic constitutive model based on hyperelasticity and multiplicative decomposition of deformation gradient tensor is extended to viscous case in a framework similar to the one that has been proposed by ponthot in an hypoelastic context in this way a very useful framework can be obtained able to deal with both rate dependent and rate independent problems in this work a review of theoretical details and numerical implementation of the model are discussed similarly to what is done in rate independent plasticity a newton raphson scheme has been used to solve the non linear consistency condition in order to compute the viscoplastic multiplier a plane strain plate with a central circular hole under tension is simulated in order to test the proposed model large deformation effects are considered in all the simulations carried out different parameters of the constitutive model are varied in order to study the sensitivity of the proposed algorithm

accuracy and stability of integration algorithms for elastoplastic constitutive relations an analysis of accuracy and stability of algorithms for the integration of elastoplastic constitutive relations is carried out in this paper reference is made to a very general internal variable formulation of plasticity and to two families of algorithms that generalize the well known trapezoidal and midpoint rules to fit the present context other integration schemes such as the radial return mean normal and closest point procedures are particular cases of this general formulation the meaning of first and second order accuracy in the presence of the plastic consistency condition is examined in detail and the criteria derived are used to identify two second order accurate members of the proposed algorithms a general methodology is also derived whereby the numerical stability properties of integration schemes can be systematically assessed with the aid of this methodology the generalized midpoint rule is seen to have far better stability properties than the generalized trapezoidal rule finally numerical examples are presented that illustrate the performance of the algorithms

integration methods for complex plastic constitutive equations abstract this paper shows new results concerning the finite element computations with complex plastic and viscoplastic constitutive equations the integration procedure then needs special numerical treatments when a large number of internal variables are present or for stiff non linearities implicit and explicit integration methods are compared the general solution proposed can be applied either in plasticity or in viscoplasticity for isotropic or anisotropic materials several options are proposed in the numerical scheme and for the completion step for the semi implicit scheme numerical tests are performed in order to compare the relative performances of the various approaches

l a l b a simplified decidability proof we give a proof of decidability of the equivalence problem for deterministic pushdown automata which simplifies that of senizergues theoret comput sci 251 2000 1

a proof of the finite field analogue of jacquet s conjecture in this paper the proof of the finite field analogue of jacquet s conjecture on local converse theorem for cuspidal representations of general linear groups is given more precisely the set of twisted gamma factors of pi big gamma pi times tau psi mid tau in scr g t 1 le t le big n over 2 big big together with a central character omega pi determine uniquely up to isomorphism the irreducible cuspidal representation pi of rm gl n bbb f q where cal g t denotes the set of irreducible generic representations of rm gl t bbb f q and bbb f q denotes a finite field of q elements

a weaker sufficient condition for the equivalence of a pair of dpda s to be decidable abstract this short paper further extends the result of tomita 1984 to have a weaker sufficient condition for the equivalence of a pair of non real time deterministic pushdown automata to be decidable

the equivalence problem for real time dpdas the equivalence problem for deterministic real time pushdown automata is shown to be decidable this result is obtained by showing that valiant s parallel stacking technique using a replacement function introduced in this paper succeeds for deterministic real time pushdown automata equivalence is also decidable for two deterministic pushdown automata one of which is real time

the bisimulation problem for equational graphs of finite out degree the bisimulation problem for equational graphs of finite out degree is shown to be decidable we reduce this problem to the eta bisimulation problem for deterministic rational vectors of boolean series on the alphabet of a deterministic pushdown automaton cal m we then exhibit a complete formal system for deducing equivalent pairs of such vectors

non linear b stability and symmetry preserving return mapping algorithms for plasticity and viscoplasticity a class of second order accurate return mapping algorithms is presented which lead to symmetric algorithmic tangent moduli and contain the classical backward euler return maps as a particular case more importantly it is shown that this class of return maps is contractive relative to the natural norm defined by the complementary helmholz free energy function b stability since the equations of classical plasticity and viscoplasticity are shown to be contractive relative to this natural norm the requirement of b stability furnishes the appropriate notion of unconditionally stable algorithms for plasticity and viscoplasticity the analysis that follows depends critically on the assumption of convexity in particular the models of plasticity and viscoplasticity considered obey the principle of maximum plastic dissipation the proposed algorithms obey the discrete counterpart of this classical principle

general solution procedures in elasto viscoplasticity constitutive relations and numerical integration algorithms for elasto viscoplastic problems are investigated a fully implicit integration scheme is adopted and the relevant expression of the consistent tangent operator for yield criteria and flow functions of arbitrary type is derived by suitably generalizing the approach exploited for rate independent plasticity this is achieved by replacing the consistency condition of plasticity with a relation between the viscoplastic consistency parameter and the flow function of the constitutive model in use the methodology adopted simplifies alternative procedures for the evaluation of consistent tangent operators which necessitate the inversion of a viscoplastic compliance operator the general expression of the consistent tangent operator is then specialized to the von mises yield criterion endowed with commonly adopted viscoplastic constitutive models numerical examples are finally presented

on a class of constitutive equations in viscoplasticity formulation and computational issues the viscoplastic constitutive model is formulated based on the existence of the dissipation potential which embodies the notion of the gauge minkowski function of the convex set a perturbation method is used for a solution of stiff differential equations characterizing the associated problem of evolution it relies on a discrete formulation of viscoplasticity which results from the regularized version of the principle of maximum plastic dissipation the operator split methodology and the newton raphson method are used to obtain the numerical solution of the discretized equations of evolution the consistent tangent modulus is expressed in a closed form as a result of the exact linearization of the discretized evolution equations for several variants of the flow potential function including some representative stiff functional forms numerical tests of the integration algorithm based on iso error maps are provided finally a numerical example is presented to illustrate the robustness and the effectiveness of the proposed approach

formulation and numerical solution of non smooth elasto visco plasticity models abstract in this work we describe in detail a model for small strain elasto visco plasticity with convex non smooth yield functions and associative nonlinear kinetic laws restricted to linear hardening using concepts of non smooth convex geometry numerical methods are developed to integrate the evolution equations of the model these algorithms are analyzed and shown to inherit a discrete dissipation inequality irrespective of the smoothness of the yield function the results are applied to models based on tresca s and drucker prager s yield criteria which include all possible types of non smoothness numerical examples are shown to illustrate the performance of the methods