dolfin team mailing list archive

["Johan Hoffman" <jhoffman@xxxxxxxxxx>]

Hi,

The best solver for the continuity equation (which is a Poisson equation
for the pressure) is a multigrid solver. In the NS solver the algebraic
multigrid solver of Hypre is used if Hypre is installed. If Hypre is not
installed a Krylov solver of Petsc is used instead.

My guess is that Hypre is installed on the Red Hat machine, and not on the
Debian machine. Then with current solver parameters (preconditioner,
tolerances, etc.) it appears that the Krylov solver does not converge for
this problem. I recommend installation of Hypre to use the algebraic
multigrid solver, or to try another preconditioner for the Krylov solver.

Best regards,
Johan


> Hi,
>
> We have run the same 2D Navier-Stokes:
> dolfin-snapshot/src/demo/solvers/navierstokes/benchmark
> in different mashines: Linux-Debian and Linux Red Hat. The
> strange thing is this: the program works perfectly in Linux Red Hat,
> but it does not work in Debian. We did not change anything,
> it is exactly the same program in different machine.
>
> The error in Debian is:
> ....
> Applying Dirichlet boundary conditions.
> Boundary condition applied to 17 degrees of freedom on the boundary.
> Solve linear system: continuity
> Solving linear system of size 3466 x 3466 (Krylov solver).
> *** Error: Krylov solver did not converge. [PETScKrylovSolver.cpp:113:
> solve()]
>
> Do you know what is the problem?
>
> Thanking in advance,
> Maziar and Murtazo
>
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