Dear petsc team, I implemented a matrix-free jacobian, and it can run sequentially. But running parallel I got the pc error like this (running with mpirun -np 2, only error from rank1 is presented here) [1]PETSC ERROR: ---------------------
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Dear petsc team,

I implemented a matrix-free jacobian, and it can run sequentially. But 
running parallel I got the pc error like this (running with mpirun -np 
2, only error from rank1 is presented here)

[1]PETSC ERROR: --------------------- Error Message 
--------------------------------------------------------------
[1]PETSC ERROR: Nonconforming object sizes
[1]PETSC ERROR: Preconditioner number of local rows 81 does not equal 
input vector size 162
[1]PETSC ERROR: See https://urldefense.us/v3/__https://petsc.org/release/faq/__;!!G_uCfscf7eWS!ahmistzr4wD3TJ0OvI0JWxB9aVSIbP78Jcs2X_6KMb4LdoR8drLB_DkHvaguhrca22RgFer0PlyUrtdfCA$ for trouble shooting.
[1]PETSC ERROR: Petsc Release Version 3.17.3, Jun 29, 2022
[1]PETSC ERROR: /home/yi/workspace/DAMASK_yi/bin/DAMASK_grid on a 
arch-linux-c-opt named carbon-x1 by yi Sun Mar 10 12:01:46 2024
[1]PETSC ERROR: Configure options --download-fftw --download-hdf5 
--with-hdf5-fortran-bindings --download-fblaslapack --download-chaco 
--download-hypre --download-metis --download-mumps --download-parmetis 
--download-scalapack --download-suitesparse --download-superlu 
--download-superlu_dist --download-triangle --download-zlib 
--download-cmake --with-cxx-dialect=C++11 --with-c2html=0 
--with-debugging=0 --with-ssl=0 --with-x=0 COPTFLAGS=-O3 CXXOPTFLAGS=-O3 
FOPTFLAGS=-O3
[1]PETSC ERROR: #1 PCApply() at 
/home/yi/App/petsc-3.17.3/src/ksp/pc/interface/precon.c:424
[1]PETSC ERROR: #2 KSP_PCApply() at 
/home/yi/App/petsc-3.17.3/include/petsc/private/kspimpl.h:376
[1]PETSC ERROR: #3 KSPInitialResidual() at 
/home/yi/App/petsc-3.17.3/src/ksp/ksp/interface/itres.c:64
[1]PETSC ERROR: #4 KSPSolve_GMRES() at 
/home/yi/App/petsc-3.17.3/src/ksp/ksp/impls/gmres/gmres.c:242
[1]PETSC ERROR: #5 KSPSolve_Private() at 
/home/yi/App/petsc-3.17.3/src/ksp/ksp/interface/itfunc.c:902
[1]PETSC ERROR: #6 KSPSolve() at 
/home/yi/App/petsc-3.17.3/src/ksp/ksp/interface/itfunc.c:1078
[1]PETSC ERROR: #7 SNESSolve_NEWTONLS() at 
/home/yi/App/petsc-3.17.3/src/snes/impls/ls/ls.c:222
[1]PETSC ERROR: #8 SNESSolve() at 
/home/yi/App/petsc-3.17.3/src/snes/interface/snes.c:4756
[1]PETSC ERROR: #9 User provided function() at User file:0

However, from snes matrix-free documentation 
(https://urldefense.us/v3/__https://petsc.org/release/manual/snes/*matrix-free-methods__;Iw!!G_uCfscf7eWS!ahmistzr4wD3TJ0OvI0JWxB9aVSIbP78Jcs2X_6KMb4LdoR8drLB_DkHvaguhrca22RgFer0Ply6ZbywOw$), it is said 
matrix-free is used with pcnone. So I assume it would not apply 
preconditioner, but it did use preconditioning probably the same as my 
matrix-free shell matrix. Here is how i initialize my shell matrix and 
the corresponding customized multiplication.

   call MatCreateShell(PETSC_COMM_WORLD,PETSC_DECIDE,PETSC_DECIDE,&
int(9*product(cells(1:2))*cells3,pPETSCINT),&
int(9*product(cells(1:2))*cells3,pPETSCINT),&
                       F_PETSc,Jac_PETSc,err_PETSc)
   call MatShellSetOperation(Jac_PETSc,MATOP_MULT,GK_op,err_PETSc)
   call SNESSetDM(SNES_mech,DM_mech,err_PETSc)
   call 
SNESSetJacobian(SNES_mech,Jac_PETSc,Jac_PETSc,PETSC_NULL_FUNCTION,0,err_PETSc)
   call SNESGetKSP(SNES_mech,ksp,err_PETSc)
   call PCSetType(pc,PCNONE,err_PETSc)

And my GK_op is like

subroutine GK_op(Jac,dF_global,output_local,err_PETSc)

   DM                                   :: dm_local
   Vec                                  :: dF_global, dF_local, output_local
   Mat                                  :: Jac
   PetscErrorCode                       :: err_PETSc

   real(pREAL), pointer,dimension(:,:,:,:) :: dF_scal, output_scal

   real(pREAL), dimension(3,3,cells(1),cells(2),cells3) :: &
     dF
   real(pREAL), dimension(3,3,cells(1),cells(2),cells3) :: &
     output

   call SNESGetDM(SNES_mech,dm_local,err_PETSc)

   call DMGetLocalVector(dm_local,dF_local,err_PETSc)
   call 
DMGlobalToLocalBegin(dm_local,dF_global,INSERT_VALUES,dF_local,err_PETSc)
   call 
DMGlobalToLocalEnd(dm_local,dF_global,INSERT_VALUES,dF_local,err_PETSc)

   call DMDAVecGetArrayReadF90(dm_local,dF_local,dF_scal,err_PETSc)
   dF = reshape(dF_scal, [3,3,cells(1),cells(2),cells3])

.......


   call DMDAVecRestoreArrayF90(dm_local,output_local,output_scal,err_PETSc)
   CHKERRQ(err_PETSc)

   call DMDAVecRestoreArrayF90(dm_local,dF_local,dF_scal,err_PETSc)
   CHKERRQ(err_PETSc)

end subroutine GK_op

I checked my cells3, it corresponds to my local size, and it seems the 
local size of dF_local is ok.

I am a bit lost here to find the reason for the preconditioner bug. 
Could you help me on this? Thanks.

Best regards,

Yi




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