MatCreateLocalRef() seems to be useful to extract submatrices from a
global matrix. But how to construct A from the beginning from its
submatrices? I.e., with MatNest, I can just do:
Mat A;
Mat matA[] = {A00, A01, NULL, A11};
MatCreateNest(PETSC_COMM_SELF, 2, NULL, 2, NULL, matA, &A);
without worrying about memory preallocations for A. Can I do the same
with MatCreateLocalRef(), or do I first have to preallocate memory for A?
Manuel
---
On 4/11/19 11:30 AM, Matthew Knepley wrote:
On Thu, Apr 11, 2019 at 2:07 AM Smith, Barry F. <[email protected]
<mailto:[email protected]>> wrote:
Matt,
You can't have some functionality in the public API for a
library and then criticize someone for using it. I looked at the
manual page for MatCreateNest() and it doesn't say in big letters
"don't use this", nor does the compiler tell the user "don't use
this". Either MatCreateNest() and/or MATNEST is so horrible it
needs to be stripped from the face of the earth or it needs to be
supported. It can't be in this nebulous state of "yeah it exists
but don't ever use it".
I agree this is a documentation problem. That is why I try to provide
complete explanations for my recommendations.
Barry
In order to support easy testing of MatCreateNest() based user
code perhaps we could add a little bit of code that allowed users
to call either
MatCreateNest() or MatNestSetSubMats() but with an option to have
it generate a regular AIJ matrix instead. For example
-mat_nest_use_aij (and MatNestUseAIJ()) This would allow users to
always write and think about their code as nested matrices but
have it "fall back" to AIJ for testing/debugging purposes.
I think we should remove MatCreateNest() completely. We should have 1
mechanism for getting submatrices for creation, not 2, so we retain
MatCreateLocalRef(). Then if -mat_type nest was specified, it gives
you back an actually submatrix, otherwise it gives a view. This would do
everything that we currently do without this horrible MatNest
interface bubbling to the top.
Matt
> On Apr 10, 2019, at 11:49 AM, Manuel Colera Rico via petsc-users
<[email protected] <mailto:[email protected]>> 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.
>
> 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.
>
> 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 <[email protected]
<mailto:[email protected]>> 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/
--
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/>
