[petsc-users] Error with KSPSetUp and MatNest

Wed Apr 10 11:57:03 CDT 2019

On Wed, Apr 10, 2019 at 12:49 PM Manuel Colera Rico <m.colera at upm.es> wrote:

> Thank you for your answer, Matt. In the MWE example attached before, both
> Nest vectors (the r.h.s. of the system and the vector of unknowns) are
> composed of the same number of blocks (2). Indeed, PETSc is able to solve
> the system if KSPSetUp() is not called, so the system/MatNest/MatVec's must
> not incompatible at all. Therefore, I wonder if I have missed to called
> something before this routine or if this is a KSPSetUp's bug.
>
I will run it.

> Of course one can always directly define a single matrix and a single
> vector, but I find it easier to work with Nest matrices and vectors.
> Moreover, I think that the moment to use them is from the beginning... once
> all the code is developed, it is very hard to switch matrices types.
>
This is not the case, and its the major reason why I want to remove
Vec/MatNest from the public interface. This is a major misconception. You
can
switch matrix types using -mat_type <type>. You can pull out submatrices
using MatGetSubmatrix() from MatAIJ just as simply as MatNest.
If you want to keep assembling submatrices, you can use

https://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/Mat/MatCreateLocalRef.html#MatCreateLocalRef

so that the assembly looks just like it does now for you, but it assembles
to an AIJ _or_ a Nest, depending on what you
choose at the command line. Then you can debug everything as AIJ, and
finally switch to Nest if you need it for optimization.

  Thanks,

     Matt

> Regards,
>
> Manuel
>
> ---
>
>
> On 4/10/19 5:41 PM, Matthew Knepley wrote:
>
> On Wed, Apr 10, 2019 at 11:29 AM Manuel Colera Rico via petsc-users <
> petsc-users at mcs.anl.gov> wrote:
>
>> Hello,
>>
>> I am trying to solve a system whose matrix is of type MatNest. If I
>> don't use KSPSetUp(), everything is fine. However, if I use that
>> routine, I get the following error:
>>
>> 0]PETSC ERROR: --------------------- Error Message
>> --------------------------------------------------------------
>> [0]PETSC ERROR: Invalid argument
>> [0]PETSC ERROR: Nest vector arguments 1 and 2 have different numbers of
>> blocks.
>>
>
> This seems self-explanatory. Nest vectors must have the same number of
> blocks to be compatible.
>
> More broadly, there should be no reason to use Nest vectors or matrices.
> It is an optimization to
> be used at the very end, only after you have profiled the code and seen
> that its important. You can
> do everything you want to do without ever touching Nest, and it looks like
> the Nest interface is a
> problem for your code right now.
>
>   Thanks,
>
>     Matt
>
>
>> [0]PETSC ERROR: See http://www.mcs.anl.gov/petsc/documentation/faq.html
>> for trouble shooting.
>> [0]PETSC ERROR: Petsc Release Version 3.11.0, unknown
>> [0]PETSC ERROR:
>> /home/manu/Documents/FEM-fluids/C-codes/CLG2-ConvectionDiffusion/Debug/CLG2-ConvectionDiffusion
>>
>> on a mcr_20190405 named mancolric by Unknown Wed Apr 10 17:20:16 2019
>> [0]PETSC ERROR: Configure options --with-cc=gcc --with-cxx=g++
>> --with-fc=gfortran COPTFLAGS="-O3 -march=native -mtune=native"
>> CXXOPTFLAGS="-O3 -march=native -mtune=native" FOPTFLAGS="-O3
>> -march=native -mtune=native" --with-debugging=0 --download-fblaslapack
>> --download--f2cblaslapack --download-mpich --download--hypre
>> --download-scalapack --download-mumps --download-suitesparse
>> --download-ptscotch --download-pastix --with-matlab --with-openmp
>> [0]PETSC ERROR: #1 VecCopy_Nest() line 68 in
>> /opt/PETSc_library/petsc-3.11.0/src/vec/vec/impls/nest/vecnest.c
>> [0]PETSC ERROR: #2 VecCopy() line 1614 in
>> /opt/PETSc_library/petsc-3.11.0/src/vec/vec/interface/vector.c
>> [0]PETSC ERROR: #3 KSPInitialResidual() line 63 in
>> /opt/PETSc_library/petsc-3.11.0/src/ksp/ksp/interface/itres.c
>> [0]PETSC ERROR: #4 KSPSolve_GMRES() line 236 in
>> /opt/PETSc_library/petsc-3.11.0/src/ksp/ksp/impls/gmres/gmres.c
>> [0]PETSC ERROR: #5 KSPSolve() line 782 in
>> /opt/PETSc_library/petsc-3.11.0/src/ksp/ksp/interface/itfunc.c
>> [0]PETSC ERROR: #6 mwe() line 55 in ../Tests/tests.c
>>
>> Please find attached a MWE (it is a slight modification of that of the
>> post opened by Ce Qin,
>> https://lists.mcs.anl.gov/pipermail/petsc-users/2015-February/024230.html,
>>
>> whose answer I have not found).
>>
>> By the way, with the newest version of PETSc, Eclipse marks as errors
>> the commands PetscFree, CHKERRQ, PETSC_COMM_SELF,... although it
>> compiles and executes well. Perhaps it is a problem related to Eclipse,
>> but this did not happen with the older versions of PETSc.
>>
>> Thanks and regards,
>>
>> Manuel
>>
>> ---
>>
>>
>
> --
> What most experimenters take for granted before they begin their
> experiments is infinitely more interesting than any results to which their
> experiments lead.
> -- Norbert Wiener
>
> https://www.cse.buffalo.edu/~knepley/
> <http://www.cse.buffalo.edu/~knepley/>
>
>

-- 
What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to which their
experiments lead.
-- Norbert Wiener

https://www.cse.buffalo.edu/~knepley/ <http://www.cse.buffalo.edu/~knepley/>
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