[petsc-users] MG Preconditioning

Sat Sep 1 14:27:28 CDT 2012

Can you send the whole calling sequence and the full error message? It's
not clear from your email how to reproduce. You might also look at
src/ksp/ksp/examples/tutorials/ex42.c which uses PCMGSetGalerkin. Did you
set the fine grid operators before calling PCSetUp()? The coarse grid
operators should have been constructed earlier in PCSetUp_MG().
On Sep 1, 2012 10:05 AM, "Gaetan Kenway" <kenway at utias.utoronto.ca> wrote:

> I believe I partially tracked down my problem. The issue arises at line
> 644 in mg.c with a call to KSPGetVecs(). This is used to get the coarse
> grid vectors for the RHS. The issue is that up until this point, the actual
> operator for mglevels[i]->smoothd have not actually been set and therefore
> it cannot get the vectors.
>
> I am using
>   call PCMGSetGalerkin(pc, PETSC_TRUE, PETScIerr)
>   call EChk(PETScIerr,__FILE__,__LINE__)
>
> with the intention of having the coarse matrices approximately
> automatically. However, from looking over the code, it appears when it is
> used in this manner, the coarse grid operators never get set. From what I
> can tell, it is only possible to create these matrices automatically if
> (pc->dm) is True which I think means that the preconditioner is derived
> from a distributed matrix.
>
> I've set my own restriction operator, but mg->galerkin has a value of -1
> in mg.c and none of the KSPSetOperators() are executed.
>
> I've also tried to generate the matrices myself using MatRARt() or
> MatPtAP, but I receive error code 56 "* /* no support for requested
> operation */" . *Is this op only implemented from matrices derived from
> from DM objects?
>
> Any other suggestions for creating the coarse grid operators manually?
>
> Thank you,
>
> Gaetan
>
>
> On Sat, Sep 1, 2012 at 12:29 AM, Jed Brown <jedbrown at mcs.anl.gov> wrote:
>
>> On Fri, Aug 31, 2012 at 11:22 PM, Gaetan Kenway <kenway at utias.utoronto.ca
>> > wrote:
>>
>>> Hi Again
>>>
>>> I also tried petsc-3.2 version and I still get the same backtrace.
>>>
>>> If its not possible to figure out where the communicator segfault is
>>> coming from its not a huge deal...I've just set the option using
>>> PetscOptionsSetValue() and then use PCSetFromOptions() to pull it back out.
>>>  That seems to work fine.
>>>
>>> Even avoiding the above problem, with the PetscOptionsSetValue I'm still
>>> receiving an error code 73 when I run the multigrid solver.  I've included
>>> the backtrace output below but its not a lot of help since the code exited
>>> cleaning using my error checking procedure
>>>
>>>  =================================================================
>>> PETSc or MPI Error. Error Code 73. Detected on Proc  0
>>> Error at line:   122 in file: solveADjointTransposePETSc.F90
>>>  =================================================================
>>>
>>> Program received signal SIGSEGV, Segmentation fault.
>>> 0xb68c98f0 in PMPI_Abort () from /usr/local/lib/libmpi.so.0
>>> (gdb) bt
>>> #0  0xb68c98f0 in PMPI_Abort () from /usr/local/lib/libmpi.so.0
>>> #1  0xb519f190 in pmpi_abort__ () from /usr/local/lib/libmpi_f77.so.0
>>> #2  0xb44c9e4c in echk (ierr=@0x49, file=..., line=@0x7a,
>>> .tmp.FILE.len_V$eb=30) at terminate.f90:154
>>> #3  0xb44bd68f in solveadjointtransposepetsc () at
>>> solveADjointTransposePETSc.F90:122
>>> #4  0xb44138a9 in f2py_rout_sumb_solveadjointtransposepetsc () from
>>> /tmp/tmpKYF_DT/sumb.so
>>> #5  0xb440fd35 in fortran_call () from /tmp/tmpKYF_DT/sumb.so
>>> #6  0x0805fd6a in PyObject_Call ()
>>> #7  0x080dd5b0 in PyEval_EvalFrameEx ()
>>> #8  0x080dfbb2 in PyEval_EvalCodeEx ()
>>> #9  0x08168f1f in ?? ()
>>> #10 0x0805fd6a in PyObject_Call ()
>>> #11 0x080dcbeb in PyEval_EvalFrameEx ()
>>> #12 0x080dfbb2 in PyEval_EvalCodeEx ()
>>> #13 0x080de145 in PyEval_EvalFrameEx ()
>>> #14 0x080dfbb2 in PyEval_EvalCodeEx ()
>>> #15 0x080dfca7 in PyEval_EvalCode ()
>>> #16 0x080fd956 in PyRun_FileExFlags ()
>>> #17 0x080fdbb2 in PyRun_SimpleFileExFlags ()
>>> #18 0x0805b6d3 in Py_Main ()
>>> #19 0x0805a8ab in main ()
>>>
>>
>>  This stack doesn't involve PETSc at all.
>>
>>
>>>
>>> Valgrid was clean right up until the end where I get the normal error
>>> message:
>>>
>>> [0]PETSC ERROR:
>>> ------------------------------------------------------------------------
>>> [0]PETSC ERROR: Caught signal number 11 SEGV: Segmentation Violation,
>>> probably memory access out of range
>>> [0]PETSC ERROR: Try option -start_in_debugger or
>>> -on_error_attach_debugger
>>> [0]PETSC ERROR: or see
>>> http://www.mcs.anl.gov/petsc/documentation/faq.html#valgrind[0]PETSCERROR: or try
>>> http://valgrind.org on GNU/linux and Apple Mac OS X to find memory
>>> corruption errors
>>> [0]PETSC ERROR: likely location of problem given in stack below
>>> [0]PETSC ERROR: ---------------------  Stack Frames
>>> ------------------------------------
>>> [0]PETSC ERROR: Note: The EXACT line numbers in the stack are not
>>> available,
>>> [0]PETSC ERROR:       INSTEAD the line number of the start of the
>>> function
>>> [0]PETSC ERROR:       is given.
>>> [0]PETSC ERROR: [0] MatGetVecs line 8142
>>> /nfs/mica/home/kenway/Downloads/petsc-3.3/src/mat/interface/matrix.c
>>> [0]PETSC ERROR: [0] KSPGetVecs line 774
>>> /nfs/mica/home/kenway/Downloads/petsc-3.3/src/ksp/ksp/interface/iterativ.c
>>> [0]PETSC ERROR: [0] PCSetUp_MG line 508
>>> /nfs/mica/home/kenway/Downloads/petsc-3.3/src/ksp/pc/impls/mg/mg.c
>>> [0]PETSC ERROR: [0] PCSetUp line 810
>>> /nfs/mica/home/kenway/Downloads/petsc-3.3/src/ksp/pc/interface/precon.c
>>> [0]PETSC ERROR: [0] KSPSetUp line 182
>>> /nfs/mica/home/kenway/Downloads/petsc-3.3/src/ksp/ksp/interface/itfunc.c
>>> [0]PETSC ERROR: [0] KSPSolve line 351
>>> /nfs/mica/home/kenway/Downloads/petsc-3.3/src/ksp/ksp/interface/itfunc.c
>>>
>>> I will try it on a different system tomorrow to see if I have any more
>>> luck.
>>>
>>> Thanks,
>>>
>>> Gaetan
>>>
>>>
>>>
>>> On Fri, Aug 31, 2012 at 11:08 PM, Jed Brown <jedbrown at mcs.anl.gov>wrote:
>>>
>>>> On Fri, Aug 31, 2012 at 10:06 PM, Matthew Knepley <knepley at gmail.com>wrote:
>>>>
>>>>> True, but the backtrace also shows that comm = 0x0 on the call to
>>>>> KSPCreate(), which
>>>>> leads me to believe that your petsc4py has not initialized PETSc, and
>>>>> therefor not
>>>>> initialized PETSC_COMM_WORLD.
>>>>>
>>>>
>>>> Could catch, maybe PetscFunctionBegin() should check that PETSc has
>>>> been initialized.
>>>>
>>>
>>>
>>
>
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