Umut Tabak <[email protected]> writes: >> Your splits were both the same, so the preconditioner was applied twice >> to the first block and zero to the second block. That made the >> preconditioner singular. > > Dear Jed, > > Thanks a lot for your time and help, attached you can find a very > challenging ill-conditioned problem: > > The first block comes from a structural problem and its size is 1490. > The second block results from a fluid discretization and its size is > 2432. So in total the coupled system is of size 3922. I created the > blocks as given in the simple problem. However, with > > ./ex3 -pc_type fieldsplit -pc_fieldsplit_type schur > -fieldsplit_1_pc_type icc -fieldsplit_1_ksp_type cg > -fieldsplit_1_pc_type icc -fieldsplit_1_ksp_type minres
You have given nearly the same options twice. Did you mean to control
the second split?
> -pc_fieldsplit_schur_factorization_type upper -ksp_monitor_true_residual
>
> The solver just hangs.
>
> The system is a symmetric system in this case given as
>
> A =
> A11 C
> C^T A22
>
> C is of size 1490X2432
>
> Could you please comment on this point for me, do I still have an error
> on the problem setup or on the usage of the options?
This is an invalid memory access and does not use ISCreateBlock correctly.
PetscInt sz1 = 1490, sz2 = 2432;
PetscInt bs = 2, n1=1, n2=1, inputindices[]={0}; /* block size is 2 */
ISCreateBlock(PETSC_COMM_SELF,sz1,n1,inputindices,
PETSC_COPY_VALUES,&is_row1);
ISCreateBlock(PETSC_COMM_SELF,sz2,n2,inputindices+n1,
PETSC_COPY_VALUES,&is_row2);
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