Besides,I test several situations.
When process=1(mpiexec -n 1),the results are right,compared with the true
results.
When process=2 or 5,both of the results are same.And from the tenth loop, it
begins the strange error Ax!=b.
When process=3 or 4,both of the results are same.And from the first loop,it
begins the error.
Thanks.
>At 2012-05-26 15:01:28,w_ang_temp <w_ang_temp at 163.com> wrote:
>Hello, Matt
> First,thanks for your help, and I have a new recognition of MPI. As you
> said(only part of a Vec is stored on each MPI process),I use
> >MPI_Send,MPI_Recv and MPI_Bcast to deal with it and get some right results.
> However,I have not yet fully solved this problem.The number of loops of the
> subroutine named PETSCSOLVE to solve Ax=b with PETSc is 20 >times.I print the
> results of each loop and find that the front 9 times are right. In the 10
> time,there is a strange error: plug the result x into the >equation I find
> that Ax!=b.
> The code and the A,x,b are shown below.So can you give me some hints? Thank
> you very much!
> Jim
> (1)code
> call MatView(A,PETSC_VIEWER_STDOUT_WORLD,ierr)
> call VecView(b,PETSC_VIEWER_STDOUT_WORLD,ierr)
> call KSPSolve(ksp,b,x,ierr)
> call VecView(x,PETSC_VIEWER_STDOUT_WORLD,ierr)
> (2)Ax=b
> A:
> type: mpiaij
> row 0: (0, 1) (1, 0) (2, 0) (3, 0) (4, 0) (5, 0) (6, 0) (7, 0) (8, 0)
> row 1: (0, 0) (1, 1) (2, 0) (3, 0) (4, 0) (5, 0) (6, 0) (7, 0) (8, 0)
> row 2: (0, 0) (1, 0) (2, -2e-06) (3, -50) (4, 0) (5, 0) (6, 0) (7,
> -50) (8, 0)
> row 3: (0, 0) (1, 0) (2, -50) (3, 1.36265e+07) (4, 0) (5, 0) (6, 0)
> (7, 1.23877e+06) (8, 0)
> row 4: (0, 0) (1, 0) (2, 0) (3, 0) (4, 1) (5, 0) (6, 0) (7, 0) (8, 0)
> row 5: (0, 0) (1, 0) (2, 0) (3, 0) (4, 0) (5, 1) (6, 0) (7, 0) (8, 0)
> row 6: (0, 0) (1, 0) (2, 0) (3, 0) (4, 0) (5, 0) (6, 1) (7, 0) (8, 0)
> row 7: (0, 0) (1, 0) (2, -50) (3, 1.23877e+06) (4, 0) (5, 0) (6, 0)
> (7, 1.36265e+07) (8, 0)
> row 8: (0, 0) (1, 0) (2, 0) (3, 0) (4, 0) (5, 0) (6, 0) (7, 0) (8, 1)
> b:
> type: mpi
> Process [0]
> 0
> 0
> -0.75
> 96949.5
> 0
> Process [1]
> 0
> -0.015
> 96949.5
> -0.015
> x:
>type: mpi
>Process [0]
> 0
> 0
> 1167.84
> 0.00819383
>0
>Process [1]
>0
> -0.00824055
> 0.00390865
> -0.00824055
>? 2012-05-22 19:33:10?"Matthew Knepley" <knepley at gmail.com> ???
>On Tue, May 22, 2012 at 5:17 AM, w_ang_temp <w_ang_temp at 163.com> wrote:
>Hello
> I am a beginner of PETSc.I find the petsc-users lists is very useful,
> however I do not know how to ask a question in it. So can you tell me? >And
> below is what I want to ask.
> I am solving Ax=b with PETSc. And I only use it in a fortran subroutine to
> get x ,then the main function of my program use x to do other >things. The
> question is that: when the process is 1(mpiexec -n 1),the result of my
> program is ok, but when the process is more than 1 the > result is wrong.
> "Wrong" is not an acceptable description. I suspect that you do not
> understand that only part of a Vec
> is stored on each MPI process. First, get the book Using MPI, and then read
> the PETSc manual
> section on vectors.
> Thanks,
> Matt
> So where could be wrong? Can you give me some hints on how I can debug?
> Thanks.
> Jim
> --
> 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
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