[petsc-users] GMRES convergence

[Barry Smith]

On Apr 18, 2013, at 11:22 AM, Colin McAuliffe <cjm2176 at columbia.edu> wrote:

> Hello all,
> 
> I am testing out a few linear solvers on a small (1052 by 1052) matrix. Using unpreconditioned GMRES with -ksp_gmres_restart 10000, GMRES still takes many times more than 1052 iterations to converge. Shouldn't it be the case that for a n by n matrix, n iterations of GMRES will give a full factorization of the matrix?

   Also run with -ksp_view and make sure that it is actually using that 10,000 restart value. (The restart size will be printed with other information about the solver).

   You can also run with -ksp_monitor_singular_value   this will you give you some idea of the conditioning of the matrix, which likely is huge.



   Barry

> Thanks
> 
> -- 
> Colin McAuliffe
> PhD Candidate
> Columbia University
> Department of Civil Engineering and Engineering Mechanics