[petsc-dev] problem with LSQR and CGNE

[Barry Smith]

  I think you mean to have 

       ierr = PCSetType(ksp3,PCNONE);

not

       ierr = PCSetType(ksp,PCNONE);

in the code fragment below. Block diagonal (which is the default) doesn't make sense for rectangular matrices.


Yes, PETSc is weak on solvers for nonsquare matrices so users would benefit from more choices. See https://bitbucket.org/petsc/petsc/wiki/pull-request-instructions-git and http://www.mcs.anl.gov/petsc/developers/developers.pdf for information on contributing code.

  Barry


> On Sep 3, 2015, at 1:21 PM, Raphaël Couturier <raphael.couturier at univ-fcomte.fr> wrote:
> 
> Hello all,
> 
> First of all, thank you Matthew and Barry for your answers in July.
> Your solution using PCKSP is fine.
> Now it works perfectly with the examples I have tried for ksp and snes. I made many tests with many processors.
> 
> I have implemented my own CGLS or LSQR method. In Petsc, I have seen that CGNE and LSQR are already implemented. However, I cannot use them because I have a problem of non square matrix.
> In previous posts, I saw that the problem can come from the preconditioner.
> In the attached code, I have my new solver (without preconditioner if I made no mistake) which is based on
> ierr = PCKSPGetKSP(pc,&sub_ksp);CHKERRQ(ierr);
> 
> and I need to use another ksp to minimize the residual (instead of my own CGLS). The matrix AS is of size (n,10) with n very large.
> I have tried with that (line 262 in the code)
> {
>        KSP ksp3;
>        ierr = KSPCreate(PETSC_COMM_WORLD, &ksp3); CHKERRQ(ierr);
>        ierr = KSPSetType(ksp3, KSPLSQR); CHKERRQ(ierr);
>        ierr = KSPSetOperators(ksp3, AS, AS); CHKERRQ(ierr);
>        ierr = KSPSetTolerances(ksp3, PETSC_DEFAULT, PETSC_DEFAULT, PETSC_DEFAULT, iter_max_minimization);
>        ierr = PCSetType(ksp,PCNONE);
>        ierr = KSPSolve(ksp3, b, Alpha); CHKERRQ(ierr);
>      }
> 
> The problem on all the processors is:
> [0]PETSC ERROR: No support for this operation for this object type
> [0]PETSC ERROR: Only square matrices supported.
> [0]PETSC ERROR: See http://www.mcs.anl.gov/petsc/documentation/faq.html for trouble shooting.
> [0]PETSC ERROR: Petsc Release Version 3.6.1, Jul, 22, 2015
> [0]PETSC ERROR: ./ex15 on a arch-linux2-c-debug named extinction by couturie Thu Sep  3 13:22:03 2015
> [0]PETSC ERROR: Configure options --download-openmpi --download-hypre --download-f2cblaslapack --with-fc=0
> [0]PETSC ERROR: #2 MatGetDiagonalBlock_MPIDense() line 78 in /home/couturie/work/petsc-3.6.1/src/mat/impls/dense/mpi/mpidense.c
> [0]PETSC ERROR: #3 MatGetDiagonalBlock() line 159 in /home/couturie/work/petsc-3.6.1/src/mat/interface/matrix.c
> [0]PETSC ERROR: #4 PCSetUp_BJacobi() line 126 in /home/couturie/work/petsc-3.6.1/src/ksp/pc/impls/bjacobi/bjacobi.c
> [0]PETSC ERROR: #5 PCSetUp() line 982 in /home/couturie/work/petsc-3.6.1/src/ksp/pc/interface/precon.c
> [0]PETSC ERROR: #6 KSPSetUp() line 332 in /home/couturie/work/petsc-3.6.1/src/ksp/ksp/interface/itfunc.c
> [0]PETSC ERROR: #7 KSPSolve() line 546 in /home/couturie/work/petsc-3.6.1/src/ksp/ksp/interface/itfunc.c
> [0]PETSC ERROR: #8 KSPSolve_TSIRM() line 269 in /home/couturie/work/petsc-3.6.1/src/ksp/ksp/impls/gmres/tsirm.c
> [0]PETSC ERROR: #9 KSPSolve() line 604 in /home/couturie/work/petsc-3.6.1/src/ksp/ksp/interface/itfunc.c
> [0]PETSC ERROR: #10 main() line 200 in /home/couturie/work/petsc-3.6.1/src/ksp/ksp/examples/tutorials/ex15.c
> 
> Do you have an idea of the problem?
> Is it a good idea to use the LSQR or CGLS method of Petsc?
> 
> 
> Moreover I have another question. Do you think that the Petsc community would be interested to use this solver. If yes, I would be glad to improve it in order to integrate it in the source.
> 
> Thanks
> 
> Raphaël
> <tsirm.c>