[petsc-users] CG+GAMG convergence issues in GHEP Krylov-Schur for some MPI runs

Tue Nov 3 05:20:43 CST 2015

I am answering the SLEPc-related questions:
- Having different number of iterations when changing the number of processes is normal.
- Yes, if you do not destroy the EPS solver, then the preconditioner would be reused.

Regarding the segmentation fault, I have no clue. Not sure if this is related to GAMG or not. Maybe running under valgrind could provide more information.

Jose

On 3/11/2015, Denis Davydov <davydden at gmail.com> wrote:
> 
> 
> Dear all, 
> 
> I experience strange convergence problems in SLEPc for GHEP with Krylov-Schur and CG + GAMG.
> The issue appears to be contingent on the number of MPI cores used. 
> Say for 8 cores there is no issue and for 4 cores there is an issue.
> When I substitute GAMG with Jacobi for the problematic number of cores -- all works. 
> 
> To be more specific, I solve Ax=\lambda Bx for a sequence of A’s where A is a function of eigenvectors.
> On each iteration step currently the eigensolver EPS is initialised from scratch. And thus should the underlying 
> ST, KSP, PC objects: -st_ksp_type cg -st_pc_type gamg -st_ksp_rtol 1e-12.
> For these particular matrices the issue appears on the 4th iteration, even though the matrix to be inverted (mass/overlap matrix)
> is the same, does not change!!!
> From my debuging info the A matrix has the same norm for CG + GAMG vs CG + Jacobi cases:
> DEAL::  frobenius_norm = 365.7
> DEAL::  linfty_norm = 19.87
> DEAL::  l1_norm = 19.87
> Just to be sure that there are no bugs on my side which would result in different mass matrices i check that
> it has the same norm for CG + GAMG vs CG + Jacobi BEFORE i start iteration:
> DEAL::  frobenius_norm = 166.4
> DEAL::  linfty_norm = 8.342
> DEAL::  l1_norm = 8.342
> All the dependent scalar quantities I calculate on each iteration are identical for the two cases, which makes me believe that 
> the solution path is the same up to the certain tolerance.
> The only output which is slightly different are the number iterations for convergence in EPS (e.g. 113 vs 108) and the 
> resulting maxing EPSComputeResidualNorm : 4.1524e-07 vs 2.9639e-08.
> 
> 
> Any ideas what could be an issue, especially given the fact that it does work for some numbers of cores and does not for other?
> Perhaps some default settings in GAMG preconditioner? Although that does not explain why it works for the first 3 iterations
> and does not on 4th as the mass matrix is unchanged...
> 
> Lastly, i suppose ideally i should keep the eigensolver context between the iterations and just update the matrices by EPSSetOperators.
> Is it correct to assume that since B matrix does not change between iterations and I use the default shift transformation with zero shift 
> (operator is B^{-1)A ), the GAMG preconditioner will not be re-initialised and thus I should save some time? 
> 
> p.s. the relevant error message is below. I have the same issues on CentOS cluster, so it is not related to OS-X.
> 
> Kind regards,
> Denis 
> 
> 
> ===
> [0]PETSC ERROR: ------------------------------------------------------------------------
> [0]PETSC ERROR: Caught signal number 15 Terminate: Some process (or the batch system) has told this process to end
> [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]PETSC ERROR: 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] KSPSolve line 510 /private/tmp/petsc20151102-50378-1t7b3in/petsc-3.6.2/src/ksp/ksp/interface/itfunc.c
> [0]PETSC ERROR: [0] STMatSolve line 148 /private/tmp/slepc20151102-3081-1xln4h0/slepc-3.6.1/src/sys/classes/st/interface/stsles.c
> [0]PETSC ERROR: [0] STApply_Shift line 33 /private/tmp/slepc20151102-3081-1xln4h0/slepc-3.6.1/src/sys/classes/st/impls/shift/shift.c
> [0]PETSC ERROR: [0] STApply line 50 /private/tmp/slepc20151102-3081-1xln4h0/slepc-3.6.1/src/sys/classes/st/interface/stsolve.c
> [0]PETSC ERROR: [0] EPSGetStartVector line 726 /private/tmp/slepc20151102-3081-1xln4h0/slepc-3.6.1/src/eps/interface/epssolve.c
> [0]PETSC ERROR: [0] EPSSolve_KrylovSchur_Symm line 41 /private/tmp/slepc20151102-3081-1xln4h0/slepc-3.6.1/src/eps/impls/krylov/krylovschur/ks-symm.c
> [0]PETSC ERROR: [0] EPSSolve line 83 /private/tmp/slepc20151102-3081-1xln4h0/slepc-3.6.1/src/eps/interface/epssolve.c
> [0]PETSC ERROR: --------------------- Error Message --------------------------------------------------------------
> [0]PETSC ERROR: Signal received
> [0]PETSC ERROR: See http://www.mcs.anl.gov/petsc/documentation/faq.html for trouble shooting.
> [0]PETSC ERROR: Petsc Release Version 3.6.2, Oct, 02, 2015 
> [0]PETSC ERROR: /Users/davydden/Desktop/work/C++/deal.ii-dft/build_debug~/dft on a real named MBP-Denis.fritz.box by davydden Tue Nov  3 07:02:47 2015
> [0]PETSC ERROR: Configure options CC=/usr/local/bin/mpicc CXX=/usr/local/bin/mpicxx F77=/usr/local/bin/mpif77 FC=/usr/local/bin/mpif90 --with-shared-libraries=1 --with-pthread=0 --with-openmp=0 --with-debugging=1 --with-ssl=0 --with-superlu_dist-include=/usr/local/opt/superlu_dist/include/superlu_dist --with-superlu_dist-lib="-L/usr/local/opt/superlu_dist/lib -lsuperlu_dist" --with-superlu-include=/usr/local/Cellar/superlu43/4.3/include/superlu --with-superlu-lib="-L/usr/local/Cellar/superlu43/4.3/lib -lsuperlu" --with-fftw-dir=/usr/local/opt/fftw --with-netcdf-dir=/usr/local/opt/netcdf --with-suitesparse-dir=/usr/local/opt/suite-sparse --with-hdf5-dir=/usr/local/opt/hdf5 --with-metis-dir=/usr/local/opt/metis --with-parmetis-dir=/usr/local/opt/parmetis --with-scalapack-dir=/usr/local/opt/scalapack --with-mumps-dir=/usr/local/opt/mumps --with-x=0 --prefix=/usr/local/Cellar/petsc/3.6.2/real --with-scalar-type=real --with-hypre-dir=/usr/local/opt/hypre --with-sundials-dir=/usr/local/opt/sundials --with-hwloc-dir=/usr/local/opt/hwloc
> [0]PETSC ERROR: #8 User provided function() line 0 in  unknown file
> --------------------------------------------------------------------------
> mpirun noticed that process rank 3 with PID 96754 on node MBP-Denis exited on signal 6 (Abort trap: 6).
> --------------------------------------------------------------------------
> 