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- Talal Rahman, Jan Valdman
- Applied Mathematics and Computation
- 2013

We propose an effective and flexible way to assemble finite element stiffness and mass matrices in MATLAB. The major loops in the code have been vectorized using the so called array operation in MATLAB, and no low level languages like the C or Fortran has been used for the purpose. The implementation is based on having the vectorization part separated, in… (More)

- Jan Valdman
- Adv. Numerical Analysis
- 2009

We consider a Poisson boundary value problem and its functional a posteriori error estimate derived by S. Repin in 1999. The estimate majorizes the H1 seminorm of the error of the discrete solution computed by FEM method and contains a free ux variable from the H div space. In order to keep the estimate sharp, a procedure for the minimization of the… (More)

- Immanuel Anjam, Jan Valdman
- Applied Mathematics and Computation
- 2015

Based on the ideas of the paper [8] by Talal Rahman and Jan Valdman we propose an effective and flexible way to assemble finite element stiffness and mass matrices in MATLAB for problems discretized by edge finite elements. Typical edge finite elements are Raviart-Thomas elements used in discretizations of H (div) spaces and Nédélec elements in… (More)

- Sergey I. Repin, Jan Valdman
- J. Num. Math.
- 2008

In this paper, we consider variational inequalities related to problems with nonlinear boundary conditions. We are focused on deriving a posteriori estimates of the difference between exact solutions of such type variational inequalities and any function lying in the admissible functional class of the problem considered. These estimates are obtained by an… (More)

Multi-yield elastoplasticity models a material with more than one plastic state and hence allows for refined approximation of irreversible deformations. Aspects of the mathematical modeling and a proof of unique existence of weak solutions can be found in part I of this paper [BCV04]. In this part II we establish a canonical time-space discretization of the… (More)

The boundary value problem representing one time step of the pri-mal formulation of elastoplasticity with positive hardening leads to a variational inequality of the second kind with some non-differentiable functional. This paper establishes an adaptive finite element algorithm for the solution of this variational inequality that yields the energy reduction… (More)

- Peter Gruber, Jan Valdman
- SIAM J. Scientific Computing
- 2009

We discuss a solution algorithm for quasi-static elastoplastic problems with hardening. Such problems can be described by a time dependent variational inequality, where the displacement and the plastic strain fields serve as primal variables. After discretization in time, one variational inequality of the second kind is obtained per time step and can be… (More)

- Jan Valdman
- 2001

The paper provides an overview of current state of technology in the field of log file analysis and stands for basics of ongoing PhD thesis. The first part covers some fundamental theory and summarizes basic goals and techniques of log file analysis. It reveals that log file analysis is an omitted field of computer science. Available papers describe… (More)

The quasi-static evolution of an elastoplastic body with a multi-surface constitutive law of linear kinematic hardening type allows the modeling of curved stress-strain relations. It generalizes classical small-strain elastoplas-ticity from one to various plastic phases. This paper presents the mathematical models and proves existence and uniqueness of the… (More)