[petsc-users] Problems about Block Jocabi and Matrix-Free Method in SNES
Matthew Knepley
knepley at gmail.com
Tue Oct 9 10:34:19 CDT 2018
On Mon, Oct 8, 2018 at 11:33 PM Yingjie Wu <yjwu16 at gmail.com> wrote:
> Dear Petsc developer:
> Hi,
>
> I've been studying Petsc recently about Precontioner and Metrix-Free, and
> I have some questions that puzzle me.
>
> 1. I want to test block Jacobi preconditioner, so I chose
> /snes/example/tutorial/ex3.c as an example. According to the reference in
> the example, the input parameters are:
> mpiexec -n 8./ex3 -nox -n 10000 -ksp_type fgmres -pc_type bjacobi
> -pc_bjacobi_blocks 4 -sub_ksp_type gmres -sub_ksp_max_it 3 -post_setsubksp
> -sub_ksp_rtol 1.e-16
>
You do not care about recursive blocks, so just use
$MPIEXEC -n 8 ./ex3 -nox -n 10000 -ksp_type fgmres -pc_type bjacobi
-pc_bjacobi_blocks 4 -sub_ksp_type gmres -sub_ksp_max_it 3 -snes_view
-ksp_view
and I get the attached output.
> I want to export each block of KSP and PC information :
> -snes_view -ksp_view
> However, the procedure is wrong and the wrong information is as follows:
>
> [0]PETSC ERROR: --------------------- Error Message
> --------------------------------------------------------------
> [0]PETSC ERROR: Arguments must have same communicators
> [0]PETSC ERROR: Different communicators in the two objects: Argument # 1
> and 2 flag 3
> [0]PETSC ERROR: [1]PETSC ERROR: --------------------- Error Message
> --------------------------------------------------------------
> [2]PETSC ERROR: --------------------- Error Message
> --------------------------------------------------------------
> [2]PETSC ERROR: [3]PETSC ERROR: --------------------- Error Message
> --------------------------------------------------------------
> [3]PETSC ERROR: Arguments must have same communicators
> [3]PETSC ERROR: [6]PETSC ERROR: --------------------- Error Message
> --------------------------------------------------------------
> [6]PETSC ERROR: Arguments must have same communicators
> [6]PETSC ERROR: Different communicators in the two objects: Argument # 1
> and 2 flag 3
> [6]PETSC ERROR: See http://www.mcs.anl.gov/petsc/documentation/faq.html
> for trouble shooting.
> [7]PETSC ERROR: --------------------- Error Message
> --------------------------------------------------------------
> [7]PETSC ERROR: Arguments must have same communicators
> [7]PETSC ERROR: Different communicators in the two objects: Argument # 1
> and 2 flag 3
> [7]PETSC ERROR: See http://www.mcs.anl.gov/petsc/documentation/faq.html
> for trouble shooting.
> [7]PETSC ERROR: Petsc Release Version 3.10.1, Sep, 26, 2018
> See http://www.mcs.anl.gov/petsc/documentation/faq.html for trouble
> shooting.
> [0]PETSC ERROR: Petsc Release Version 3.10.1, Sep, 26, 2018
> [0]PETSC ERROR: ./ex3 on a arch-linux2-c-debug named yjwu-XPS-8910 by yjwu
> Mon Oct 8 22:35:34 2018
> [0]PETSC ERROR: Configure options --with-cc=gcc --with-cxx=g++
> --with-fc=gfortran --download-mpich --download-fblaslapack
> [0]PETSC ERROR: #1 KSPView() line 118 in
> /home/yjwu/petsc-3.10.1/src/ksp/ksp/interface/itcreate.c
> [0]PETSC ERROR: #2 PCView_BJacobi() line 232 in
> /home/yjwu/petsc-3.10.1/src/ksp/pc/impls/bjacobi/bjacobi.c
> [0]PETSC ERROR: #3 PCView() line 1651 in
> /home/yjwu/petsc-3.10.1/src/ksp/pc/interface/precon.c
> [1]PETSC ERROR: Arguments must have same communicators
> [1]PETSC ERROR: Different communicators in the two objects: Argument # 1
> and 2 flag 3
> [1]PETSC ERROR: See http://www.mcs.anl.gov/petsc/documentation/faq.html
> for trouble shooting.
> [1]PETSC ERROR: Petsc Release Version 3.10.1, Sep, 26, 2018
> [1]PETSC ERROR: ./ex3 on a arch-linux2-c-debug named yjwu-XPS-8910 by yjwu
> Mon Oct 8 22:35:34 2018
> [1]PETSC ERROR: Configure options --with-cc=gcc --with-cxx=g++
> --with-fc=gfortran --download-mpich --download-fblaslapack
> [1]PETSC ERROR: #1 KSPView() line 118 in
> /home/yjwu/petsc-3.10.1/src/ksp/ksp/interface/itcreate.c
> Arguments must have same communicators
> [2]PETSC ERROR: Different communicators in the two objects: Argument # 1
> and 2 flag 3
> [2]PETSC ERROR: See http://www.mcs.anl.gov/petsc/documentation/faq.html
> for trouble shooting.
>
> If I want to get the information of KSP and PC in each block, what should
> I do?
>
> 2. There is a requirement in my program to use Matrix-Free method to
> approximate Jacobian matrix by finite difference of residual function in
> solving nonlinear equations. But I'll also provide an analytic( incomplete,
> some terms are missing or approximate) for preconditioning. Because my
> problem is about a large set of equations composed of several physical
> fields, I want to use block Jacobian precondition for each subfield(block),
> and ILU sub_pc for each subfield. After reading the Users'Guide, I found
> that using - snex_mf_operator can do the above, so I added:
> - snes_mf_operator
>
You need to be careful what matrix you are adding values to in your
FormJacobian() routine. The primal matrix J is of type MFFD (finite
difference)
and thus cannot accept values. You put your approximate values in the
preconditioner M.
Thanks,
Matt
> after the example above. However, the procedure is wrong and does not seem
> to support this.
> The wrong information is:
>
> [1]PETSC ERROR: --------------------- Error Message
> --------------------------------------------------------------
> [2]PETSC ERROR: --------------------- Error Message
> --------------------------------------------------------------
> [2]PETSC ERROR: No support for this operation for this object type
> [2]PETSC ERROR: Mat type mffd
> [2]PETSC ERROR: [3]PETSC ERROR: [4]PETSC ERROR: ---------------------
> Error Message --------------------------------------------------------------
> [4]PETSC ERROR: No support for this operation for this object type
> [4]PETSC ERROR: Mat type mffd
> [4]PETSC ERROR: See http://www.mcs.anl.gov/petsc/documentation/faq.html
> for trouble shooting.
> [4]PETSC ERROR: Petsc Release Version 3.10.1, Sep, 26, 2018
> [6]PETSC ERROR: --------------------- Error Message
> --------------------------------------------------------------
> [6]PETSC ERROR: No support for this operation for this object type
> [6]PETSC ERROR: Mat type mffd
> [6]PETSC ERROR: See http://www.mcs.anl.gov/petsc/documentation/faq.html
> for trouble shooting.
> [6]PETSC ERROR: Petsc Release Version 3.10.1, Sep, 26, 2018
> [6]PETSC ERROR: ./ex3 on a arch-linux2-c-debug named yjwu-XPS-8910 by yjwu
> Mon Oct 8 23:01:57 2018
> [6]PETSC ERROR: Configure options --with-cc=gcc --with-cxx=g++
> --with-fc=gfortran --download-mpich --download-fblaslapack
> [0]PETSC ERROR: --------------------- Error Message
> --------------------------------------------------------------
> [0]PETSC ERROR: No support for this operation for this object type
> [0]PETSC ERROR: Mat type mffd
> [0]PETSC ERROR: See http://www.mcs.anl.gov/petsc/documentation/faq.html
> for trouble shooting.
> [0]PETSC ERROR: Petsc Release Version 3.10.1, Sep, 26, 2018
> [0]PETSC ERROR: ./ex3 on a arch-linux2-c-debug named yjwu-XPS-8910 by yjwu
> Mon Oct 8 23:01:57 2018
> [0]PETSC ERROR: Configure options --with-cc=gcc --with-cxx=g++
> --with-fc=gfortran --download-mpich --download-fblaslapack
> [0]PETSC ERROR: #1 MatSetValues() line 1330 in
> /home/yjwu/petsc-3.10.1/src/mat/interface/matrix.c
> [1]PETSC ERROR: No support for this operation for this object type
> [1]PETSC ERROR: Mat type mffd
> [1]PETSC ERROR: See http://www.mcs.anl.gov/petsc/documentation/faq.html
> for trouble shooting.
>
> If I want to implement matrix-free and block jacobi precondition in my
> program, what do I need to pay attention or add ?
>
> The second question is very important for my research and I hope to get
> your answer.
>
> Thanks,
> Yingjie
>
--
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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