# Tagged Questions

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198 views

### A numerical GMRES example

I'm having trouble understanding how GMRES works. I've read the part in Saad's book and a few others but still I am confused. Can someone provide me a numerical example to understand it better? Or if ...
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### What factors are relevant when deciding between GMRES and schur complement solves?

Suppose I have a linear system  \left\lbrack \begin{array}{cc} M_1& S\\ S^{\mathrm{T}}& M_2 \end{array} \right\rbrack \left\lbrack \begin{array}{c} X\\ Y\end{array} \right\rbrack= \...
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### MATLAB: code for restarted gmres

I have a question about Matlab and restarted gmres. I would like to use gmres.m provided here. This code seems to be a popular for the scientific computation ...
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### OpenMP threaded nonlinear solver for complex numbers

Problem: I have translated Jacobian-Free Newton-Krylov solver written by C. T. Kelley to Fortran and now want to parallelize it on shared-memory system with OpenMP. In addition, I want to precondition ...
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### High quality flexible GMRES (FGMRES) implementation

What are the best FGMRES implementations in various languages/frameworks? In particular, are there any good quality Matlab implementations? I am referring to the variation of GMRES where a changing ...
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### GMRES: Making the matrix square without solving for boundaries

How do we define the matrix for GMRES, if we do not want to solve the boundary elements but only the interior ones. I am using pentagonal elements so in a row there are 6 elements (cell itself + 5 ...
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### preconditioning a krylov method with another krylov method

In method like gmres or bicgstab it could be attractive to use another krylov method as a preconditioner. After all they are easy to implement in a matrix-free way and in a parallel environment. For ...
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### Not enough memory for GMRES

After realizing that Gauss-Seidel is extremely slow for my simulation, i wanted to try GMRES and luckily found the C++ code here without diving into the theory. The size of the matrix in my case is <...
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### Petsc solver problem

I have to resolve the linear equation Ax = B in which A is not symmetrical, either definite positive. I used the solver GMRES of Petsc. It seems to work well but with the same configuration (initial ...
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### GMRES implementations

I am looking for simple GMRES implementations. Unfortunately, I have a few requirements: should be C or Fortran, Fortran preferred needs a license that permits inclusion in an MIT/BSD licensed ...
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### Problems where Conjugate gradient works much better than GMRES

I am interested in cases where Conjugate gradient works much better than GMRES method. In general, CG is preferable choice in many cases of SPD (symmetric-positive-definite) because it requires less ...
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### Parameter selection difficulty in GMRES

we are using a first order implicit finite volume code for simulation of incompressible flows. At its core, the code utilizes a (non-preconditioned) GMRES method for solving linear systems given in ...
800 views

### GMRES Matlab 'tol' parameter

I need to use GMRES solver in MATLAB, and I need to play around with the codes parameters and I had a very simple question about its usage. The documentation of the solver here mentions a parameter <...