[petsc-dev] MUMPS silent errors

[Zhang, Junchao]

I checked with MUMPS developers and they said MUMPS would gave a new error code if a previous step failed. That is nice.  Hong, I find code like this in mumps.c, which does not follow the 'no error if failure' rule, does it?

   mumps->id.job = JOB_SOLVE;
   PetscMUMPS_c(mumps);
   if (mumps->id.INFOG(1) < 0) SETERRQ1(PETSC_COMM_SELF,PETSC_ERR_LIB,"Error reported by MUMPS in solve phase: INFOG(1)=%d\n",mumps->id.INFOG(1));


________________________________
From: Zhang, Junchao
Sent: Wednesday, October 10, 2018 10:54:21 PM
To: Smith, Barry F.
Cc: petsc-dev
Subject: Re: [petsc-dev] MUMPS silent errors


What is embarrassing is the user sent me beautiful -log_view outputs and began doing performance comparison. The whole thing is meaningless only because he forgot to check the converged reason on a direct solver.


MUMPS manual has "A call to MUMPS with JOB=2 must be preceded by a call with JOB=1 on the same instance", and similar languages for other phases.  It implies we at least should not call MatSolve_MUMPS with failed factorization since it might crash the code.

________________________________
From: Smith, Barry F.
Sent: Wednesday, October 10, 2018 6:41:20 PM
To: Zhang, Junchao
Cc: petsc-dev
Subject: Re: [petsc-dev] MUMPS silent errors


  I looked at the code and it is handled in the PETSc way. The user should not expect KSP to error just because it was unable to solve a linear system; they should be calling KSPGetConvergedReason() after KSPSolve() to check that the solution was computed successfully.

   Barry


> On Oct 10, 2018, at 2:12 PM, Zhang, Junchao <jczhang at mcs.anl.gov> wrote:
>
> I met a case where MUMPS numeric factorization returned an error code -9 in mumps->id.INFOG(1) but A->erroriffailure was false in the following code in mumps.c
> 1199: PetscErrorCode MatFactorNumeric_MUMPS(Mat F,Mat A,const MatFactorInfo *info)
> 1200:
> {
> ...
>
> 1227:   PetscMUMPS_c(mumps);
> 1228:   if
>  (mumps->id.INFOG(1) < 0) {
>
> 1229:     if
>  (A->erroriffailure) {
>
> 1230:       SETERRQ2(PETSC_COMM_SELF,PETSC_ERR_LIB,"Error reported by MUMPS in numerical factorization phase: INFOG(1)=%d, INFO(2)=%d\n"
> ,mumps->id.INFOG(1),mumps->id.INFO(2));
>
> 1231:     } else
>  {
>
> 1232:       if (mumps->id.INFOG(1) == -10) { /* numerically singular matrix */
> 1233:         PetscInfo2(F,"matrix is numerically singular, INFOG(1)=%d, INFO(2)=%d\n"
> ,mumps->id.INFOG(1),mumps->id.INFO(2));
>
> 1234:
>         F->factorerrortype = MAT_FACTOR_NUMERIC_ZEROPIVOT;
>
>
> The code continued to KSPSolve and finished successfully (with wrong answer). The user did not call KSPGetConvergedReason() after KSPSolve. I found I had  to either add -ksp_error_if_not_converged or call KSPSetErrorIfNotConverged(ksp,PETSC_TRUE) to make the code fail.
> Is it expected?  In my view, it is dangerous. If MUMPS fails in one stage, PETSc should not proceed to the next stage because it may hang there.

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