[petsc-users] Problems about PCtype bjacobi
Mark Adams
mfadams at lbl.gov
Wed Nov 7 10:01:54 CST 2018
On Wed, Nov 7, 2018 at 10:16 AM Yingjie Wu via petsc-users <
petsc-users at mcs.anl.gov> wrote:
> Dear Petsc developer:
> Hi,
> Recently, I'm solving the problems of nonlinear systems of PDEs, I
> encountered some problems about precondition and wanted to seek help.
>
> 1.I set the precondition matrix in SNES as MPIAIJ in the program, and then
> use Matrix Free method to solve my problem. The log information of the
> program is as follows:
>
> SNES Object: 1 MPI processes
> type: newtonls
> maximum iterations=50, maximum function evaluations=100000000
> tolerances: relative=1e-08, absolute=1e-50, solution=1e-08
> total number of linear solver iterations=177
> total number of function evaluations=371
> norm schedule ALWAYS
> SNESLineSearch Object: 1 MPI processes
> type: bt
> interpolation: cubic
> alpha=1.000000e-04
> maxstep=1.000000e+08, minlambda=1.000000e-12
> tolerances: relative=1.000000e-08, absolute=1.000000e-15,
> lambda=1.000000e-08
> maximum iterations=40
> KSP Object: 1 MPI processes
> type: gmres
> restart=30, using Classical (unmodified) Gram-Schmidt
> Orthogonalization with no iterative refinement
> happy breakdown tolerance 1e-30
> maximum iterations=10000, initial guess is zero
> tolerances: relative=0.01, absolute=1e-50, divergence=10000.
> left preconditioning
> using PRECONDITIONED norm type for convergence test
> PC Object: 1 MPI processes
> type: bjacobi
> number of blocks = 1
> Local solve is same for all blocks, in the following KSP and PC
> objects:
> KSP Object: (sub_) 1 MPI processes
> type: preonly
> maximum iterations=10000, initial guess is zero
> tolerances: relative=1e-05, absolute=1e-50, divergence=10000.
> left preconditioning
> using NONE norm type for convergence test
> PC Object: (sub_) 1 MPI processes
> type: bjacobi
> number of blocks = 1
> Local solve is same for all blocks, in the following KSP and PC
> objects:
> KSP Object: (sub_sub_) 1 MPI processes
> type: preonly
> maximum iterations=10000, initial guess is zero
> tolerances: relative=1e-05, absolute=1e-50, divergence=10000.
> left preconditioning
> using NONE norm type for convergence test
> PC Object: (sub_sub_) 1 MPI processes
> type: ilu
> out-of-place factorization
> 0 levels of fill
> tolerance for zero pivot 2.22045e-14
> matrix ordering: natural
> factor fill ratio given 1., needed 1.
> Factored matrix follows:
> Mat Object: 1 MPI processes
> type: seqaij
> rows=961, cols=961
> package used to perform factorization: petsc
> total: nonzeros=4129, allocated nonzeros=4129
> total number of mallocs used during MatSetValues calls
> =0
> not using I-node routines
> linear system matrix = precond matrix:
> Mat Object: 1 MPI processes
> type: seqaij
> rows=961, cols=961
> total: nonzeros=4129, allocated nonzeros=4805
> total number of mallocs used during MatSetValues calls =0
> not using I-node routines
> linear system matrix = precond matrix:
> Mat Object: 1 MPI processes
> type: mpiaij
> rows=961, cols=961
> total: nonzeros=4129, allocated nonzeros=9610
> total number of mallocs used during MatSetValues calls =0
> not using I-node (on process 0) routines
> linear system matrix followed by preconditioner matrix:
> Mat Object: 1 MPI processes
> type: mffd
> rows=961, cols=961
> Matrix-free approximation:
> err=1.49012e-08 (relative error in function evaluation)
> Using wp compute h routine
> Does not compute normU
> Mat Object: 1 MPI processes
> type: mpiaij
> rows=961, cols=961
> total: nonzeros=4129, allocated nonzeros=9610
> total number of mallocs used during MatSetValues calls =0
> not using I-node (on process 0) routines
>
> Although parallel matrix is used, it runs on a single processor. Because
> of the use of parallel matrices, the overall precondition scheme should be
> bjacobi, and then build a KSP for each block (there is only one block in my
> program). Therefore, there will be a sub KSP object in the PC information.
> But in the above information, a subsubksp is also embedded in the sub KSP
> object. I don't understand the reason for this KSP. Please help me answer.
>
It looks like you are setting the sub PC type to bjacobi and it has a sub
(sub) PC.
>
> 2. Bjacobi is a precondition method in theory. Why is there a subsystem of
> linear equations solver object ksp? In my understanding, precondition is a
> matrix decomposition method, and there is no linear equations，. Therefore,
> there should be no subKSP here.
>
> 3.when I assemble precondition matrix, I used MatSetVales.
>
> idleft = row - 1 ;
>
> idright = row + 1 ;
>
> idup = row + 20;
>
> iddown = row - 20;
>
>
>
> /*phi1 field*/
>
> v[1] = - 1.0 / ( dx * dx / (2* 1.267) + dx * dx / (2* 1.267 ) ) ;
> col[1] = idleft;
>
> v[2] = - 1.0 / ( dx * dx / (2* 1.267) + dx * dx / (2* 1.267 ) ) ;
> col[2] = idright;
>
> v[3] = - 1.0/ ( dy * dy / (2* 1.267) + dy * dy / (2* 1.267 ) ) ;
> col[3] = iddown;
>
> v[4] = - 1.0 / ( dy * dy / (2* 1.267) + dy * dy / (2* 1.267 ) ) ;
> col[4] = idup;
>
> v[0] = v[1] + v[2] + v[3] + v[4] + v[0] ; col[0] = row;
>
> ierr = MatSetValues(B,1,&row,5,col,v,INSERT_VALUES);CHKERRQ(ierr);
>
>
There must be junk in "col" somehow. I don't see anything wrong with this
code. Print out the values of "col" before the MatSetValues call.
> The wrong information is:
>
> [0]PETSC ERROR: --------------------- Error Message
> --------------------------------------------------------------
> [0]PETSC ERROR: Argument out of range
> [0]PETSC ERROR: Column too large: col 1077215232 max 960
> [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: ./ex217 on a arch-linux2-c-debug named yjwu-XPS-8910 by
> yjwu Wed Nov 7 09:52:22 2018
> [0]PETSC ERROR: Configure options --with-cc=gcc --with-cxx=g++
> --with-fc=gfortran --download-mpich --download-fblaslapack
> [0]PETSC ERROR: #1 MatSetValues_SeqAIJ() line 442 in
> /home/yjwu/petsc-3.10.1/src/mat/impls/aij/seq/aij.c
> [0]PETSC ERROR: #2 MatSetValues() line 1349 in
> /home/yjwu/petsc-3.10.1/src/mat/interface/matrix.c
> [0]PETSC ERROR: #3 FormJacobian() line 272 in
> /home/yjwu/petsc-3.10.1/src/snes/examples/tutorials/ex217.c
> [0]PETSC ERROR: #4 SNESComputeJacobian() line 2555 in
> /home/yjwu/petsc-3.10.1/src/snes/interface/snes.c
> [0]PETSC ERROR: #5 SNESSolve_NEWTONLS() line 222 in
> /home/yjwu/petsc-3.10.1/src/snes/impls/ls/ls.c
> [0]PETSC ERROR: #6 SNESSolve() line 4396 in
> /home/yjwu/petsc-3.10.1/src/snes/interface/snes.c
> [0]PETSC ERROR: #7 main() line 108 in
> /home/yjwu/petsc-3.10.1/src/snes/examples/tutorials/ex217.c
>
> This seems to be a very obvious question, but I don't know how to solve
> it.
>
> Thanks for your continuous help,
> Yingjie
>
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