[petsc-users] why a certain option cannot be used
Sun, Hui
hus003 at ucsd.edu
Thu Jul 17 00:11:05 CDT 2014
Dave, and other PETSc users, sorry for bothering you all again. However continuing this topic, I have another question. Within this ex70.c, there is a user defined schur complement StokesSetupApproxSchur, defined as
/* Schur complement approximation: myS = A11 - A10 diag(A00)^(-1) A01 */
The preconditioner here can be written out explicitly as a matrix, and is not changed between iterations. Each time it is applied to the residue is simply matrix times vector. However, if I want to define a preconditioner which is allowed to vary between iterations, for example, if I need to solve a linear system each time I apply the preconditioner to the residue, then is there a way I can do this? Any hint will be greatly appreciated. Thank you very much!
Best,
Hui
________________________________
From: Dave May [dave.mayhem23 at gmail.com]
Sent: Wednesday, July 16, 2014 3:40 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 the fieldsplit preconditioning type. The choices are
-pc_fieldsplit_type <MULTIPLICATIVE> (choose one of) ADDITIVE MULTIPLICATIVE SYMMETRIC_MULTIPLICATIVE SPECIAL SCHUR
Maybe what you want to run is the following
./ex70 -ksp_view -pc_type fieldsplit -fieldsplit_0_pc_type jacobi -fieldsplit_1_pc_type jacobi -pc_fieldsplit_type SCHUR -pc_fieldsplit_schur_precondition user
The option " -fieldsplit_1_user_pc" seems meaningless to me.
I don't see anything in ex70.c which would cause this option to have any effect. The lines
ierr = PetscOptionsHasName(NULL, "-user_pc", &s.userPC);CHKERRQ(ierr);
ierr = PetscOptionsHasName(NULL, "-user_ksp", &s.userKSP);CHKERRQ(ierr);
imply that the option -user_pc and -user_ksp are meaningful and modify how the schur complement preconditioner will be configured. The first option triggers this setup to occur;
if (s->userPC) {
ierr = PCFieldSplitSchurPrecondition(pc, PC_FIELDSPLIT_SCHUR_PRE_USER, s->myS);CHKERRQ(ierr);
}
the second option will force this setup to occur
if (s->userKSP) {
ierr = PCSetUp(pc);CHKERRQ(ierr);
ierr = PCFieldSplitGetSubKSP(pc, &n, &subksp);CHKERRQ(ierr);
ierr = KSPSetOperators(subksp[1], s->myS, s->myS, SAME_PRECONDITIONER);CHKERRQ(ierr);
ierr = PetscFree(subksp);CHKERRQ(ierr);
}
On 17 July 2014 00:24, Sun, Hui <hus003 at ucsd.edu<mailto:hus003 at ucsd.edu>> wrote:
Thank you Dave. It does give me the other options. However I want to be able to use the user defined fieldsplit_1_pc_type. In example ex70.c, there is a user defined Schur complement preconditioner. I want to use that. Then how should I set the values for the options?
I tried to see which values could be set by typing
./ex70 -pc_type fieldsplit -help 2>/dev/null | grep -A5 fieldsplit_1_pc
And I get the following output:
-fieldsplit_1_pc_type <bjacobi>: Preconditioner (one of) none jacobi pbjacobi bjacobi sor lu shell mg
eisenstat ilu icc cholesky asm gasm ksp composite redundant nn mat fieldsplit galerkin exotic hmpi asa cp lsc redistribute svd gamg tfs (PCSetType)
-fieldsplit_1_pc_use_amat: <FALSE> use Amat (instead of Pmat) to define preconditioner in nested inner solves (PCSetUseAmat)
Block Jacobi options
-fieldsplit_1_pc_bjacobi_blocks <-1>: Total number of blocks (PCBJacobiSetTotalBlocks)
Krylov Method (KSP) options -------------------------------------------------
-fieldsplit_1_ksp_type <preonly>: 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)
-fieldsplit_1_ksp_max_it <10000>: Maximum number of iterations (KSPSetTolerances)
-fieldsplit_1_ksp_rtol <1e-05>: Relative decrease in residual norm (KSPSetTolerances)
I cannot find anything here about the user defined pc. Do you have any idea what might be the choice?
________________________________
From: Dave May [dave.mayhem23 at gmail.com<mailto:dave.mayhem23 at gmail.com>]
Sent: Wednesday, July 16, 2014 3:11 PM
To: Sun, Hui
Cc: Matthew Knepley; petsc-users at mcs.anl.gov<mailto:petsc-users at mcs.anl.gov>
Subject: Re: [petsc-users] why a certain option cannot be used
To see all the fieldsplit options, run with
./ex70 -pc_type fieldsplit -help
-help will only display the options relevant to the current configuration of your KSP and PC.
On 17 July 2014 00:10, Dave May <dave.mayhem23 at gmail.com<mailto:dave.mayhem23 at gmail.com>> wrote:
Run with
-help
On 17 July 2014 00:07, Sun, Hui <hus003 at ucsd.edu<mailto:hus003 at ucsd.edu>> wrote:
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<mailto: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<mailto: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<http://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<http://UrlBlockedError.aspx>]
Sent: Wednesday, July 16, 2014 2:32 PM
To: Sun, Hui
Cc: petsc-users at mcs.anl.gov<http://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<http://UrlBlockedError.aspx>> wrote:
On Wed, Jul 16, 2014 at 4:22 PM, Sun, Hui <hus003 at ucsd.edu<http://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<http://UrlBlockedError.aspx>]
Sent: Wednesday, July 16, 2014 2:16 PM
To: Sun, Hui
Cc: petsc-users at mcs.anl.gov<http://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<http://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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