[petsc-users] Slepc eigen value solver gives strange behavior

[Jose E. Roman]

El 06/04/2011, a las 05:21, Gong Ding escribió:

> Dear Jose,
> will you please also take a look at the SVD code for smallest singular value?
> It seems work except the time consuming SVDCyclicSetExplicitMatrix routine.
> However, I wonder if there exist some more clever method.

I think it is correct.
Jose

> 
>  // SVD solver for smallest singular value
>  SVD            svd_s;
>  EPS            eps_s;
>  ST             st_s;
>  KSP            ksp_s;
>  PC             pc_s;
> 
>  PetscErrorCode ierr;
> 
>  // Create singular value solver context
>  ierr = SVDCreate(PETSC_COMM_WORLD, &svd_s);
> 
>  // Set operator
>  ierr = SVDSetOperator(svd_s, J);
> 
> 
>  // small singular value use eigen value solver on Cyclic Matrix
>  ierr = SVDSetWhichSingularTriplets(svd_s, SVD_SMALLEST);
>  ierr = SVDSetType(svd_s, SVDCYCLIC);
>  ierr = SVDCyclicSetExplicitMatrix(svd_s, PETSC_TRUE); // <-----time consuming
>  // shift-and-invert spectral transformation to enhance convergence of eigenvalues near zero
>  ierr = SVDCyclicGetEPS(svd_s, &eps_s);
>  ierr = EPSSetType(eps_s, EPSKRYLOVSCHUR);
>  ierr = EPSGetST(eps_s, &st_s);
>  ierr = STSetType(st_s, STSINVERT);
> 
>  ierr = STGetKSP(st_s, &ksp_s);
>  ierr = KSPGetPC(ksp_s, &pc_s);
>  // since we have to deal with bad conditioned problem, we choose direct solver whenever possible
> 
>  // direct solver as preconditioner
>  ierr = KSPSetType (ksp_s, (char*) KSPGMRES); assert(!ierr);
>  // superlu which use static pivot seems very stable
>  ierr = PCSetType  (pc_s, (char*) PCLU); assert(!ierr);
>  ierr = PCFactorSetMatSolverPackage (pc_s, "superlu"); assert(!ierr);
> 
>  // Set solver parameters at runtime
>  ierr = SVDSetFromOptions(svd_s);  assert(!ierr);
> 
>  ierr = SVDSetUp(svd_s); assert(!ierr);
> 
>  PetscReal sigma_large=1, sigma_small=1;
>  PetscInt nconv;
>  PetscReal error;
> 
>  // find the smallest singular value
>  SVDSolve(svd_s);