<div dir="ltr">Dear Matthew, <br><br>PCFIELDSPLIT seems a little more complex, I will try that. <br><br>I tried some different preconditioners, only lu can get right results. <br><br>With some pc, some wrong results can be obtained, such as the following one. <br>
<br>tutorials]$ time ./ex78 -Ain A_in -rhs rhs -solu solu -noshift -pc_type hypre -pc_hypre_type parasails -ksp_gmres_restart 600 -ksp_rtol 1e-5 -ksp_typ gmres<br><br> Read matrix in ascii format ...<br>m: 288399, n: 288399, nz: 4023176 <br>
read A completed <br> rowNumber[0] = 13 <br> rowNumber[1] = 13 <br> rowNumber[2] = 19 <br> read A is complete ! <br><br> Read rhs in ascii format ...<br><br> Read exact solution in ascii format ...<br><br> Accuracy of the reading data: | b - A*u |_2 : 3321.15 <br>
<br> Iteration number is : 38 <br><br>real 0m11.977s<br>user 0m11.752s<br>sys 0m0.216s<br><br>The iteration should have converged, while converge to some wrong results. <br><br>Regards, <br>Kai <br><br><div class="gmail_quote">
<blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
Message: 8<br>
Date: Thu, 10 Nov 2011 14:10:14 +0000<br>
From: Matthew Knepley <<a href="mailto:knepley@gmail.com">knepley@gmail.com</a>><br>
Subject: Re: [petsc-users] Any suggestion for this kinds of matrix?<br>
To: PETSc users list <<a href="mailto:petsc-users@mcs.anl.gov">petsc-users@mcs.anl.gov</a>><br>
Message-ID:<br>
<<a href="mailto:CAMYG4GnxR2A%2BTcVzmsiOgD4wp4P%2Ba_GRnPBg1YQKz7bJT5XiDw@mail.gmail.com">CAMYG4GnxR2A+TcVzmsiOgD4wp4P+a_GRnPBg1YQKz7bJT5XiDw@mail.gmail.com</a>><br>
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<br>
On Thu, Nov 10, 2011 at 1:48 PM, Bao Kai <<a href="mailto:paeanball@gmail.com">paeanball@gmail.com</a>> wrote:<br>
<br>
> Dear all,<br>
><br>
> I have been trying with PETSC to solve the linear system from mixed finite<br>
> element method.<br>
><br>
> The pattern of the matrix is as the following, but due to the irregular<br>
> boundary involved, the matrix A is not strictly symmetric.<br>
><br>
> A dt* C<br>
><br>
> C^T 0<br>
><br>
> As a result of the matrix pattern, the diagonal entries of the<br>
> bottom-right portion are all zero.<br>
><br>
> I am just wondering if there are any suggestion of the type of the solver<br>
> and preconditioner for this kinds of linear system? Thank you very much.<br>
><br>
> When I tried to solve the system with PETSC, I got the following<br>
> information. ( PCType PCASM, KSPType, KSPFGMRES )<br>
><br>
<br>
ILU is jsut not going to work for this type of matrix (a saddle point). I<br>
suggest reading about PCFIELDSPLIT.<br>
<br>
Matt<br>
<br>
<br>
> [0]PETSC ERROR: --------------------- Error Message<br>
> ------------------------------------<br>
> [0]PETSC ERROR: Object is in wrong state!<br>
> [0]PETSC ERROR: Matrix is missing diagonal entry 288398!<br>
> [0]PETSC ERROR:<br>
> ------------------------------------------------------------------------<br>
> [0]PETSC ERROR: Petsc Release Version 3.2.0, Patch 4, Sun Oct 23 12:23:18<br>
> CDT 2011<br>
> [0]PETSC ERROR: See docs/changes/index.html for recent updates.<br>
> [0]PETSC ERROR: See docs/faq.html for hints about trouble shooting.<br>
> [0]PETSC ERROR: See docs/index.html for manual pages.<br>
> [0]PETSC ERROR:<br>
> ------------------------------------------------------------------------<br>
> [0]PETSC ERROR: Libraries linked from<br>
> /home/baok/software/petsc-3.2-p4/arch-linux2-c-debug-withhypre/lib<br>
> [0]PETSC ERROR: Configure run at Thu Nov 10 11:49:03 2011<br>
> [0]PETSC ERROR: Configure options --download-hypre=yes<br>
> [0]PETSC ERROR:<br>
> ------------------------------------------------------------------------<br>
> [0]PETSC ERROR: MatILUFactorSymbolic_SeqAIJ_ilu0() line 1636 in<br>
> /home/baok/software/petsc-3.2-p4/src/mat/impls/aij/seq/aijfact.c<br>
> [0]PETSC ERROR: MatILUFactorSymbolic_SeqAIJ() line 1740 in<br>
> /home/baok/software/petsc-3.2-p4/src/mat/impls/aij/seq/aijfact.c<br>
> [0]PETSC ERROR: MatILUFactorSymbolic() line 6092 in<br>
> /home/baok/software/petsc-3.2-p4/src/mat/interface/matrix.c<br>
> [0]PETSC ERROR: PCSetUp_ILU() line 216 in<br>
> /home/baok/software/petsc-3.2-p4/src/ksp/pc/impls/factor/ilu/ilu.c<br>
> [0]PETSC ERROR: PCSetUp() line 819 in<br>
> /home/baok/software/petsc-3.2-p4/src/ksp/pc/interface/precon.c<br>
> [0]PETSC ERROR: KSPSetUp() line 260 in<br>
> /home/baok/software/petsc-3.2-p4/src/ksp/ksp/interface/itfunc.c<br>
> [0]PETSC ERROR: PCSetUpOnBlocks_ASM() line 339 in<br>
> /home/baok/software/petsc-3.2-p4/src/ksp/pc/impls/asm/asm.c<br>
> [0]PETSC ERROR: PCSetUpOnBlocks() line 852 in<br>
> /home/baok/software/petsc-3.2-p4/src/ksp/pc/interface/precon.c<br>
> [0]PETSC ERROR: KSPSetUpOnBlocks() line 154 in<br>
> /home/baok/software/petsc-3.2-p4/src/ksp/ksp/interface/itfunc.c<br>
> [0]PETSC ERROR: KSPSolve() line 380 in<br>
> /home/baok/software/petsc-3.2-p4/src/ksp/ksp/interface/itfunc.c<br>
> [0]PETSC ERROR: main() line 261 in src/ksp/ksp/examples/tutorials/ex78.c<br>
><br>
><br>
> Best Regards,<br>
> Kai<br>
><br>
><br>
<br>
<br>
--<br>
What most experimenters take for granted before they begin their<br>
experiments is infinitely more interesting than any results to which their<br>
experiments lead.<br>
-- Norbert Wiener<br>
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