[petsc-users] ex12 poisson solver

[Matthew Knepley]

On Mon, Oct 9, 2017 at 12:40 PM, Justin Chang <jychang48 at gmail.com> wrote:

> You need this additional command line argument: -petscspace_order 1
>

Justin is correct. By default, it is P0, which would be a purely
discontinuous solution to Laplace, without
jump terms.

  Thanks,

    Matt


> On Mon, Oct 9, 2017 at 9:02 AM, David Fuentes <fuentesdt at gmail.com> wrote:
>
>>
>> Hi,
>>
>> I'm trying to use petsc 3.8.0 with ex12.c example to setup a poisson
>> solver: http://www.mcs.anl.gov/petsc/petsc-current/src/snes/examples
>> /tutorials/ex12.c.html
>>
>> I seem to be getting zeros in my jacobian with this example?
>> I attached a debugger and the assembly routines seems ok... but am
>> getting zero jacobian somewhere along the way to the MatAssembly...
>> Am I missing something with the command line arguments ?
>>
>>
>>
>> $ ./ex12 -snes_type ksponly  -snes_monitor -snes_converged_reason
>> -ksp_converged_reason -ksp_monitor -ksp_rtol 1.e-6 -pc_type jacobi -info
>> -info_exclude null,pc,vec
>> ------------------------------------------------------------
>> --------------
>> [[55310,1],0]: A high-performance Open MPI point-to-point messaging module
>> was unable to find any relevant network interfaces:
>>
>> Module: OpenFabrics (openib)
>>   Host: SCRGP2
>>
>> Another transport will be used instead, although this may result in
>> lower performance.
>> ------------------------------------------------------------
>> --------------
>> [0] MatAssemblyEnd_SeqAIJ(): Matrix size: 8 X 8; storage space: 0
>> unneeded,8 used
>> [0] MatAssemblyEnd_SeqAIJ(): Number of mallocs during MatSetValues() is 0
>> [0] MatAssemblyEnd_SeqAIJ(): Maximum nonzeros in any row is 1
>> [0] MatCheckCompressedRow(): Found the ratio (num_zerorows
>> 0)/(num_localrows 8) < 0.6. Do not use CompressedRow routines.
>> [0] MatSeqAIJCheckInode(): Found 8 nodes out of 8 rows. Not using Inode
>> routines
>> [0] DMGetDMSNES(): Creating new DMSNES
>> [0] DMGetDMKSP(): Creating new DMKSP
>>   0 SNES Function norm 1.414213562373e+00
>> [0] MatAssemblyEnd_SeqAIJ(): Matrix size: 8 X 8; storage space: 0
>> unneeded,8 used
>> [0] MatAssemblyEnd_SeqAIJ(): Number of mallocs during MatSetValues() is 0
>> [0] MatAssemblyEnd_SeqAIJ(): Maximum nonzeros in any row is 1
>> [0] MatCheckCompressedRow(): Found the ratio (num_zerorows
>> 0)/(num_localrows 8) < 0.6. Do not use CompressedRow routines.
>> [0] SNESComputeJacobian(): Rebuilding preconditioner
>>     0 KSP Residual norm 1.414213562373e+00
>>     1 KSP Residual norm 1.414213562373e+00
>> [0] KSPGMRESBuildSoln(): Likely your matrix or preconditioner is
>> singular. HH(it,it) is identically zero; it = 0 GRS(it) = 1.41421
>>   Linear solve did not converge due to DIVERGED_BREAKDOWN iterations 1
>> [0] SNESSolve_KSPONLY(): iter=0, number linear solve failures 1 greater
>> than current SNES allowed, stopping solve
>> Nonlinear solve did not converge due to DIVERGED_LINEAR_SOLVE iterations 0
>> Number of SNES iterations = 0
>> L_2 Error: 0.751285
>>
>>
>> configured with: ./config/configure.py --with-shared-libraries
>> --with-clanguage=c++ --CFLAGS='-g -O0' --CXXFLAGS='-g -O0'
>> --download-ctetgen  --download-triangle --with-debugging=yes
>> --with-exodusii-lib=[/usr/lib/x86_64-linux-gnu/libexoIIv2.so]
>> --with-netcdf-lib=[/usr/lib/libnetcdf.so] --with-netcdf-include=/usr/include
>> --with-hdf5-include=/usr/include/hdf5/serial/
>> --with-hdf5-lib=[/usr/lib/x86_64-linux-gnu/hdf5/serial/libhdf5.so]
>> --with-c2html=0 --with-exodusii-include=/usr/include
>>
>>
>> thanks!
>> David
>>
>>
>>
>


-- 
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.caam.rice.edu/~mk51/>
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