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[Anders Logg <question108259@xxxxxxxxxxxxxxxxxxxxx>]

Question #108259 on DOLFIN changed:
https://answers.launchpad.net/dolfin/+question/108259

Anders Logg posted a new comment:
On Thu, Apr 29, 2010 at 04:14:21PM -0000, Murtazo Nazarov wrote:
> Question #108259 on DOLFIN changed:
> https://answers.launchpad.net/dolfin/+question/108259
>
>     Status: Answered => Solved
>
> Murtazo Nazarov confirmed that the question is solved:
> Yes, it seems hypre in my solver does not converge only in the first
> iteration. Before it was just a warning, but with the latest dolfin it
> stoped since it is assumed that it is an error.
>
> Here I made a test for the same problem using the following lines:
>
>    solver = KrylovSolver("gmres")
>    solver.parameters["monitor_convergence"] = True
>    solver.parameters["error_on_nonconvergence"] = False
> ..
>
> "Old" dolfin gives:
> ....
> Applying boundary conditions to linear system.
> Applying boundary conditions to linear system.
> Solving linear system of size 4184 x 4184 (PETSc Krylov solver).
>   0 KSP preconditioned resid norm 2.663347782311e+02 true resid norm 1.371810197831e+01 ||Ae||/||Ax|| 7.817835153984e+08
> *** Warning: Krylov solver did not converge (PETSc reason -4).
> PETSc Krylov solver (gmres, hypre) failed to converge in 0 iterations.
> ...
>
> and the latest dolfin gives:
>
> Applying boundary conditions to linear system.
> Applying boundary conditions to linear system.
> Solving linear system of size 4184 x 4184 (PETSc Krylov solver).
>   0 KSP preconditioned resid norm 6.346755394553e+02 true resid norm 3.269022479529e+01 ||Ae||/||Ax|| 3.675021072956e+08
> *** Warning: Krylov solver did not converge (PETSc reason -4).
> PETSc Krylov solver (gmres, hypre) failed to converge in 0 iterations.
>
> It happened because of the luck of stabilization in startup.
>
> It is nice to know about the latest flags in the parameter list for the
> Krylov solver.
>
> murtazo

ok, good to know. So there is nothing wrong with the solver.

I suggest you let "error_on_nonconvergence" stay true, otherwise you
will not see when it fails.

--
Anders

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