PETSc is slowing down in C++? again

[xiaoyin ji]

Hi,

I cannot include running options like -ksp_monitor in my program as
it's not a simple petsc code. However, after testing the ksp examples
I've found similar problem.

Here is the code I'm testing src/ksp/ksp/examples/tutorials/ex2.c

What I've done is add a loop of 10000 steps between MatCreate and
MatDestory (right before PetscFinalize), and print the time for each
loop. The time will increase exponentially just like my program.
Moreover, if I narrow the loop so that only ksp create and destory are
included, solving time does not change. -ksp_monitor option shows that
ksp loop is running fine, however I cannot use this option with the
time test as print out will change the loop time significantly.

It seems to me that either MatDestory or VecDestory does not clear
everything well in C++ codes( in Fortran codes they work well).
Besides, instead of directly call petsc functions, I've also created a
class which contains petsc mat and ksp utilities, and create/destroy
the object of this class for each loop. However problem still exists.

Best,
Xiaoyin Ji

On Thu, Sep 3, 2009 at 8:34 AM, xiaoyin ji<sapphire.jxy at gmail.com> wrote:
> Hi,
>
> Here are the print outs
>
> for the very beginning, average time is about 0.8sec for the ksp solver
> KSP Object:
>  type: bicg
>  maximum iterations=10000, initial guess is zero
>  tolerances:  relative=1e-07, absolute=1e-50, divergence=10000
>  left preconditioning
> PC Object:
>  type: bjacobi
>    block Jacobi: number of blocks = 16
>    Local solve is same for all blocks, in the following KSP and PC objects:
>  KSP Object:(sub_)
>    type: preonly
>    maximum iterations=10000, initial guess is zero
>    tolerances:  relative=1e-05, absolute=1e-50, divergence=10000
>    left preconditioning
>  PC Object:(sub_)
>    type: ilu
>      ILU: 0 levels of fill
>      ILU: factor fill ratio allocated 1
>      ILU: tolerance for zero pivot 1e-12
>      ILU: using diagonal shift to prevent zero pivot
>      ILU: using diagonal shift on blocks to prevent zero pivot
>           out-of-place factorization
>           matrix ordering: natural
>      ILU: factor fill ratio needed 1
>           Factored matrix follows
>          Matrix Object:
>            type=seqaij, rows=5672, cols=5672
>            package used to perform factorization: petsc
>            total: nonzeros=39090, allocated nonzeros=39704
>              not using I-node routines
>    linear system matrix = precond matrix:
>    Matrix Object:
>      type=seqaij, rows=5672, cols=5672
>      total: nonzeros=39090, allocated nonzeros=39704
>        not using I-node routines
>  linear system matrix = precond matrix:
>  Matrix Object:
>    type=mpiaij, rows=90746, cols=90746
>    total: nonzeros=636378, allocated nonzeros=1279114
>      not using I-node (on process 0) routines
> Norm of error 48.144, Iterations 137
>
> After 4000 steps, solver takes 7.5sec
>
> KSP Object:
>  type: bicg
>  maximum iterations=10000, initial guess is zero
>  tolerances:  relative=1e-07, absolute=1e-50, divergence=10000
>  left preconditioning
> PC Object:
>  type: bjacobi
>    block Jacobi: number of blocks = 16
>    Local solve is same for all blocks, in the following KSP and PC objects:
>  KSP Object:(sub_)
>    type: preonly
>    maximum iterations=10000, initial guess is zero
>    tolerances:  relative=1e-05, absolute=1e-50, divergence=10000
>    left preconditioning
>  PC Object:(sub_)
>    type: ilu
>      ILU: 0 levels of fill
>      ILU: factor fill ratio allocated 1
>      ILU: tolerance for zero pivot 1e-12
>      ILU: using diagonal shift to prevent zero pivot
>      ILU: using diagonal shift on blocks to prevent zero pivot
>           out-of-place factorization
>           matrix ordering: natural
>      ILU: factor fill ratio needed 1
>           Factored matrix follows
>          Matrix Object:
>            type=seqaij, rows=5672, cols=5672
>            package used to perform factorization: petsc
>            total: nonzeros=39090, allocated nonzeros=39704
>              not using I-node routines
>    linear system matrix = precond matrix:
>    Matrix Object:
>      type=seqaij, rows=5672, cols=5672
>      total: nonzeros=39090, allocated nonzeros=39704
>        not using I-node routines
>  linear system matrix = precond matrix:
>  Matrix Object:
>    type=mpiaij, rows=90746, cols=90746
>    total: nonzeros=636378, allocated nonzeros=1279114
>      not using I-node (on process 0) routines
> Norm of error 48.7467, Iterations 132
>
>
> The iterations are similar, solving time is actually increasing
> exponentially, and the matrix should not be too complicated here as
> the PETSc in Fortran solved this in 1sec.
>
> By the way, will there be a way to set a PETSc vector directly into a
> preconditioner for the ksp solver?
>
> Thanks!
>
> Best,
> Xiaoyin Ji
>
> Department of Materials Science and Engineering
> North Carolina State University
>