[petsc-users] why a certain option cannot be used

Wed Jul 16 17:07:44 CDT 2014

Thank you Dave, it does solve the problem. Another question is: since some options like

-fieldsplit_0_pc_type

does not show up if I type

./ex70 -help

how then can I have a complete list of all the options?

Best,
Hui

________________________________
From: Dave May [dave.mayhem23 at gmail.com]
Sent: Wednesday, July 16, 2014 2:57 PM
To: Sun, Hui
Cc: Matthew Knepley; petsc-users at mcs.anl.gov
Subject: Re: [petsc-users] why a certain option cannot be used

You need to specify on the command line
-pc_type fieldsplit -fieldsplit_0_pc_type xxx -fieldsplit_1_pc_type yyy

Where xxx and yyy are the desired preconditioners for the (1,1) block and (2,2) block. Note that the default PC (ilu(0)) applied to both splits will fail for this example.

The comments in the code are misleading and incorrect. Without the option -pc_type fieldsplit, all fieldsplit options have no effect.

When debugging solvers, always run with - ksp_view (as Matt recommends)

On Wednesday, 16 July 2014, Sun, Hui <hus003 at ucsd.edu<mailto:hus003 at ucsd.edu>> wrote:
No I don't think I'm using fieldsplitting although I want to use it. The output of

./ex70 -nx 32 -ny 48 -fieldsplit_1_pc_type jacobi -ksp_view

is the following:

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: none

  linear system matrix = precond matrix:

  Matrix Object:   1 MPI processes

    type: nest

    rows=4608, cols=4608

      Matrix object:

        type=nest, rows=2, cols=2

        MatNest structure:

        (0,0) : prefix="a00_", type=mpiaij, rows=3072, cols=3072

        (0,1) : prefix="a01_", type=mpiaij, rows=3072, cols=1536

        (1,0) : prefix="a10_", type=mpiaij, rows=1536, cols=3072

        (1,1) : prefix="a11_", type=mpiaij, rows=1536, cols=1536

 residual u = 2.6315e-05

 residual p = 0.000229872

 residual [u,p] = 0.000231373

 discretization error u = 0.00633503

 discretization error p = 0.121534

 discretization error [u,p] = 0.121699

WARNING! There are options you set that were not used!

WARNING! could be spelling mistake, etc!

Option left: name:-fieldsplit_1_pc_type value: jacobi

________________________________
From: Sun, Hui
Sent: Wednesday, July 16, 2014 2:40 PM
To: Matthew Knepley
Cc: petsc-users at mcs.anl.gov<UrlBlockedError.aspx>
Subject: RE: [petsc-users] why a certain option cannot be used

Thank you Matt. I've corrected it to

./ex70 -nx 32 -ny 48 -fieldsplit_1_pc_type jacobi

However the output is still:

residual u = 2.6315e-05

 residual p = 0.000229872

 residual [u,p] = 0.000231373

 discretization error u = 0.00633503

 discretization error p = 0.121534

 discretization error [u,p] = 0.121699

WARNING! There are options you set that were not used!

WARNING! could be spelling mistake, etc!

Option left: name:-fieldsplit_1_pc_type value: jacobi

If I type

./ex70 -help | grep fieldsplit_1_

the output is that nothing coming out.

________________________________
From: Matthew Knepley [knepley at gmail.com<UrlBlockedError.aspx>]
Sent: Wednesday, July 16, 2014 2:32 PM
To: Sun, Hui
Cc: petsc-users at mcs.anl.gov<UrlBlockedError.aspx>
Subject: Re: [petsc-users] why a certain option cannot be used

On Wed, Jul 16, 2014 at 4:25 PM, Matthew Knepley <knepley at gmail.com<UrlBlockedError.aspx>> wrote:
On Wed, Jul 16, 2014 at 4:22 PM, Sun, Hui <hus003 at ucsd.edu<UrlBlockedError.aspx>> wrote:
Thank you Matt for answering, however even with that I don't think it works. For example, the command

./ex70 -nx 32 -ny 48 -fieldsplit_1_type jacobi

You have mistyped. Look carefully at my last message:

  -fieldsplit_1_pc_type jacobi

I also want to note that you can see all the available options with -help. It does produce
a lot of output, but you can segregate it by prefix ("fieldsplit_1_"). You can also see the
prefix of each solver component using -ksp_view.

  Matt

     Matt

gives me the following output

residual u = 2.6315e-05

 residual p = 0.000229872

 residual [u,p] = 0.000231373

 discretization error u = 0.00633503

 discretization error p = 0.121534

 discretization error [u,p] = 0.121699

WARNING! There are options you set that were not used!

WARNING! could be spelling mistake, etc!

Option left: name:-fieldsplit_1_type value: jacobi

Furthermore, if I look into the possible options with keyword fieldsplit involved by the command:

./ex70 -help | grep -A5 fieldsplit

I get this output:

eisenstat ilu icc cholesky asm gasm ksp composite redundant nn mat fieldsplit galerkin exotic hmpi asa cp lsc redistribute svd gamg tfs (PCSetType)

  -pc_use_amat: <FALSE> use Amat (instead of Pmat) to define preconditioner in nested inner solves (PCSetUseAmat)

Krylov Method (KSP) options -------------------------------------------------

  -ksp_type <gmres>: Krylov method (one of) cg groppcg pipecg cgne nash stcg gltr richardson

      chebyshev gmres tcqmr bcgs ibcgs fbcgs fbcgsr bcgsl cgs tfqmr cr pipecr lsqr preonly qcg bicg fgmres minres symmlq lgmres lcd gcr pgmres specest dgmres (KSPSetType)

  -ksp_max_it <10000>: Maximum number of iterations (KSPSetTolerances)

So I don't see any option that's similar to -fieldsplit_1_type.

Hui

________________________________
From: Matthew Knepley [knepley at gmail.com<UrlBlockedError.aspx>]
Sent: Wednesday, July 16, 2014 2:16 PM
To: Sun, Hui
Cc: petsc-users at mcs.anl.gov<UrlBlockedError.aspx>
Subject: Re: [petsc-users] why a certain option cannot be used

On Wed, Jul 16, 2014 at 4:09 PM, Sun, Hui <hus003 at ucsd.edu<UrlBlockedError.aspx>> wrote:
I want to solve Stokes equation using user defined schur complement preconditioner. So I'm reading and testing snes/examples/tutorial/ex55.c, and ex70.c. In these examples, there are comments about the usage, for example:

mpiexec -n 2 ./stokes -nx 32 -ny 48 -fieldsplit_1_user_pc.

However the option -fieldsplit_1_user_pc is not recognized by the executable. The output of the above command is:

This ("user_pc") is just a mnemonic. What it means is that you can use any PC in this slot. What he should have written is

  -fieldsplit_1_pc_type <user pc>

  Thanks,

     Matt

 residual u = 2.6315e-05

 residual p = 0.000229872

 residual [u,p] = 0.000231373

 discretization error u = 0.00633503

 discretization error p = 0.121534

 discretization error [u,p] = 0.121699

WARNING! There are options you set that were not used!

WARNING! could be spelling mistake, etc!

Option left: name:-fieldsplit_1_user_pc (no value)

I'm wondering what's going on. Is that because I need some specific options during my configuring of the package? By the way, the version of PETSc I'm using is 3.4.4.

Best,

Hui

--
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

--
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

--
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
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