[petsc-users] Question with setting up KSP solver parameters.
Song Gao
song.gao2 at mail.mcgill.ca
Fri May 2 17:29:24 CDT 2014
Thanks for your quick reply. What confused me is that why would the code works fine if I reset the gmres restart number by recalling kspgmressetrestart just before kspsolve?
Sent from my iPhone
> On May 2, 2014, at 6:03 PM, "Barry Smith" <bsmith at mcs.anl.gov> wrote:
>
>
> Your shell matrix is buggy in some way. Whenever the residual norm jumps like crazy at a restart it means that something is wrong with the operator.
>
> Barry
>
>> On May 2, 2014, at 4:41 PM, Song Gao <song.gao2 at mail.mcgill.ca> wrote:
>>
>> Dear PETSc users,
>>
>> I'm solving a linear system in KSP and trying to setup the solver in codes. But I feel strange because my codes don't converge unless I call KSPGMRESSetRestart twice.
>>
>> My codes looks like
>>
>> call KSPSetOperators ( pet_solv, pet_mat_mf_shell, pet_matp, DIFFERENT_NONZERO_PATTERN, ierpetsc )
>> call KSPSetType ( pet_solv, 'gmres', ierpetsc )
>> call KSPGMRESSetRestart ( pet_solv, 30, ierpetsc )
>> call KSPGetPC ( pet_solv, pet_precon, ierpetsc )
>> call PCSetType ( pet_precon, 'asm', ierpetsc )
>> call PCASMSetOverlap ( pet_precon, 1, ierpetsc )
>> call KSPSetUp ( pet_solv, ierpetsc )
>> call PCASMGetSubKSP ( pet_precon, n_local, first_local, pet_solv_sub, ierpetsc ) ! n_local is one
>> call KSPGetPC ( pet_solv_sub(1), pet_precon_sub, ierpetsc )
>> call PCSetType ( pet_precon_sub, 'jacobi', ierpetsc )
>> call PCJacobiSetUseRowMax ( pet_precon_sub, ierpetsc )
>> call KSPSetFromOptions ( pet_solv, ierpetsc )
>> call KSPGMRESSetRestart ( pet_solv, 29, ierpetsc ) ! adding this line, the codes converge
>> call KSPSolve ( pet_solv, pet_rhsp, pet_solup, ierpetsc )
>>
>> runing with 1 CPU WITHOUT the line with red color and the codes don't converge
>>
>> runtime options: -ksp_monitor_true_residual -ksp_view
>> 0 KSP preconditioned resid norm 6.585278940829e+00 true resid norm 9.619278462343e-03 ||r(i)||/||b|| 1.000000000000e+00
>> 1 KSP preconditioned resid norm 6.585278219510e+00 true resid norm 9.619278462343e-03 ||r(i)||/||b|| 1.000000000000e+00
>> 2 KSP preconditioned resid norm 2.198638170622e+00 true resid norm 1.365132713014e-01 ||r(i)||/||b|| 1.419163317039e+01
>> 3 KSP preconditioned resid norm 1.599896387215e+00 true resid norm 1.445988845022e-01 ||r(i)||/||b|| 1.503219654865e+01
>> .......
>> 28 KSP preconditioned resid norm 4.478466011191e-01 true resid norm 1.529879309381e-01 ||r(i)||/||b|| 1.590430420920e+01
>> 29 KSP preconditioned resid norm 4.398129572260e-01 true resid norm 1.530132924055e-01 ||r(i)||/||b|| 1.590694073413e+01
>> 30 KSP preconditioned resid norm 2.783227613716e+12 true resid norm 1.530369123550e-01 ||r(i)||/||b|| 1.590939621450e+01
>>
>> KSP Object: 1 MPI processes
>> type: gmres
>> GMRES: restart=30, using Classical (unmodified) Gram-Schmidt Orthogonalization with no iterative refinement
>> GMRES: happy breakdown tolerance 1e-30
>> maximum iterations=10000, initial guess is zero
>> tolerances: relative=1e-05, absolute=1e-50, divergence=10000
>> left preconditioning
>> using PRECONDITIONED norm type for convergence test
>> PC Object: 1 MPI processes
>> type: asm
>> Additive Schwarz: total subdomain blocks = 1, amount of overlap = 1
>> Additive Schwarz: restriction/interpolation type - RESTRICT
>> [0] number of local blocks = 1
>> Local solve info for each block is in the following KSP and PC objects:
>> - - - - - - - - - - - - - - - - - -
>> [0] local block number 0, size = 22905
>> KSP Object: (sub_) 1 MPI processes
>> type: preonly
>> maximum iterations=10000, initial guess is zero
>> tolerances: relative=1e-05, absolute=1e-50, divergence=10000
>> left preconditioning
>> using NONE norm type for convergence test
>> PC Object: (sub_) 1 MPI processes
>> type: jacobi
>> linear system matrix = precond matrix:
>> Matrix Object: 1 MPI processes
>> type: seqbaij
>> rows=22905, cols=22905, bs=5
>> total: nonzeros=785525, allocated nonzeros=785525
>> total number of mallocs used during MatSetValues calls =0
>> block size is 5
>> - - - - - - - - - - - - - - - - - -
>> linear system matrix followed by preconditioner matrix:
>> Matrix Object: 1 MPI processes
>> type: shell
>> rows=22905, cols=22905
>> Matrix Object: 1 MPI processes
>> type: seqbaij
>> rows=22905, cols=22905, bs=5
>> total: nonzeros=785525, allocated nonzeros=785525
>> total number of mallocs used during MatSetValues calls =0
>> block size is 5
>> WARNING: zero iteration in iterative solver
>>
>> runing with 1 CPU WITH the line with red color and the codes converge
>>
>> runtime options: -ksp_monitor_true_residual -ksp_view
>> 0 KSP preconditioned resid norm 6.585278940829e+00 true resid norm 9.619278462343e-03 ||r(i)||/||b|| 1.000000000000e+00
>> 1 KSP preconditioned resid norm 2.566248171026e+00 true resid norm 4.841043870812e-03 ||r(i)||/||b|| 5.032647604250e-01
>> 2 KSP preconditioned resid norm 1.410418402651e+00 true resid norm 3.347509391208e-03 ||r(i)||/||b|| 3.480000505561e-01
>> 3 KSP preconditioned resid norm 9.665409287757e-01 true resid norm 2.289877121679e-03 ||r(i)||/||b|| 2.380508195748e-01
>> 4 KSP preconditioned resid norm 4.469486152454e-01 true resid norm 1.283813398084e-03 ||r(i)||/||b|| 1.334625463968e-01
>> 5 KSP preconditioned resid norm 2.474889829653e-01 true resid norm 7.956009139680e-04 ||r(i)||/||b|| 8.270900120862e-02
>> ............
>> 24 KSP preconditioned resid norm 9.518780877620e-05 true resid norm 6.273993696172e-07 ||r(i)||/||b|| 6.522312167937e-05
>> 25 KSP preconditioned resid norm 6.837876679998e-05 true resid norm 4.612861071815e-07 ||r(i)||/||b|| 4.795433555514e-05
>> 26 KSP preconditioned resid norm 4.864361942316e-05 true resid norm 3.394754589076e-07 ||r(i)||/||b|| 3.529115621682e-05
>> KSP Object: 1 MPI processes
>> type: gmres
>> GMRES: restart=29, using Classical (unmodified) Gram-Schmidt Orthogonalization with no iterative refinement
>> GMRES: happy breakdown tolerance 1e-30
>> maximum iterations=10000, initial guess is zero
>> tolerances: relative=1e-05, absolute=1e-50, divergence=10000
>> left preconditioning
>> using PRECONDITIONED norm type for convergence test
>> PC Object: 1 MPI processes
>> type: asm
>> Additive Schwarz: total subdomain blocks = 1, amount of overlap = 1
>> Additive Schwarz: restriction/interpolation type - RESTRICT
>> [0] number of local blocks = 1
>> Local solve info for each block is in the following KSP and PC objects:
>> - - - - - - - - - - - - - - - - - -
>> [0] local block number 0, size = 22905
>> KSP Object: (sub_) 1 MPI processes
>> type: preonly
>> maximum iterations=10000, initial guess is zero
>> tolerances: relative=1e-05, absolute=1e-50, divergence=10000
>> left preconditioning
>> using NONE norm type for convergence test
>> PC Object: (sub_) 1 MPI processes
>> type: jacobi
>> linear system matrix = precond matrix:
>> Matrix Object: 1 MPI processes
>> type: seqbaij
>> rows=22905, cols=22905, bs=5
>> total: nonzeros=785525, allocated nonzeros=785525
>> total number of mallocs used during MatSetValues calls =0
>> block size is 5
>> - - - - - - - - - - - - - - - - - -
>> linear system matrix followed by preconditioner matrix:
>> Matrix Object: 1 MPI processes
>> type: shell
>> rows=22905, cols=22905
>> Matrix Object: 1 MPI processes
>> type: seqbaij
>> rows=22905, cols=22905, bs=5
>> total: nonzeros=785525, allocated nonzeros=785525
>> total number of mallocs used during MatSetValues calls =0
>> block size is 5
>> WARNING: zero iteration in iterative solver
>>
>>
>> What would be my error here? Thank you.
>
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