[petsc-users] SLEPc fails with POWER ITERATION method

[Jose E. Roman]

The power method only works with which=EPS_LARGEST_MAGNITUDE (or which=EPS_TARGET_MAGNITUDE if doing shift-and-invert). The rationale is that the power iteration converges to the dominant eigenvalue (the one with largest absolute value).

Jose


> El 7/8/2015, a las 18:21, Xujun Zhao <xzhao99 at gmail.com> escribió:
> 
> Hi all,
> 
> I am solving the max eigenvalue of a Shell matrix using SLEPc. the Shell operation is set MATOP_MULT with user-defined function u = M*f. It works with the Krylov-Schur and Arnoldi method, but fails when I use Power Iteration method and several others. This is strange, because some of those are supposed to work with any type of problem.
> 
> I also wrote a power iteration algorithm by myself, and it works well and obtains the same results with that from Krylov_Schur. I am curious why this doesn't work is SLEPc. The following are my code and error messages:
> 
> ----------------------------------------------------------------------------------
>   ierr = MatSetFromOptions(M);      CHKERRQ(ierr);
>   ierr = MatShellSetOperation(M,MATOP_MULT,(void(*)())_MatMult_Stokes);CHKERRQ(ierr);
> 
>   ierr = PetscPrintf(PETSC_COMM_WORLD,"\n");
>   printf("--->test: n = %d, N = %d, rank = %d\n",n, N, (int)rank);
> 
> 
>   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
>    Create the eigensolver and set various options
>    - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
> 
>   ierr = EPSCreate(PETSC_COMM_WORLD,&eps);  CHKERRQ(ierr);
>   ierr = EPSSetOperators(eps,M,NULL);       CHKERRQ(ierr);
>   ierr = EPSSetProblemType(eps,EPS_HEP);   CHKERRQ(ierr);
> 
> 
>   // EPSKRYLOVSCHUR(Default)/EPSARNOLDI/
>   // does NOT work: EPSPOWER/EPSLANCZOS/EPSSUBSPACE
>   ierr = EPSSetType(eps,EPSPOWER);          CHKERRQ(ierr);
> 
> 
>   /*  Select portion of spectrum */
> 
>   if(option=="smallest")  // LOBPCG for smallest eigenvalue problem!
>   { ierr = EPSSetWhichEigenpairs(eps,EPS_SMALLEST_REAL);CHKERRQ(ierr);  }
>   else if(option=="largest")
>   { ierr = EPSSetWhichEigenpairs(eps,EPS_LARGEST_REAL); CHKERRQ(ierr);  }
>   else
>   { ierr = EPSSetFromOptions(eps);  CHKERRQ(ierr);  }
>   // end if-else
> 
> 
>   // Set the tolerance and maximum iteration
>   ierr = EPSSetTolerances(eps,  tol,  maxits);  CHKERRQ(ierr);
>   ierr = PetscPrintf(PETSC_COMM_WORLD,"EPS tol = %f, maxits = %d\n",tol,maxits);CHKERRQ(ierr);
> 
> 
>   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
>    Solve the eigensystem and get the solution
>    - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
> 
>   ierr = PetscPrintf(PETSC_COMM_WORLD,"EPS solve starts ...\n");CHKERRQ(ierr);
>   ierr = EPSSolve(eps);CHKERRQ(ierr);
> 
> ----------------------------------------------------------------------------------
> 
> 
> EPS tol = 0.000001, maxits = 100
> 
> EPS solve starts ...
> 
> [0]PETSC ERROR: --------------------- Error Message --------------------------------------------------------------
> 
> [0]PETSC ERROR: Wrong value of eps->which
> 
> [0]PETSC ERROR: See http://www.mcs.anl.gov/petsc/documentation/faq.html for trouble shooting.
> 
> [0]PETSC ERROR: Petsc Release Version 3.5.4, May, 23, 2015 
> 
> [0]PETSC ERROR: ./example-opt on a arch-darwin-c-opt named mcswl121.mcs.anl.gov by xzhao Fri Aug  7 10:31:38 2015
> 
> [0]PETSC ERROR: Configure options --with-cc=gcc-4.9 --with-cxx=g++-4.9 --with-fc=gfortran-4.9 --with-cxx-dialect=C++11 --download-mpich --download-fblaslapack --download-scalapack --download-mumps --download-superlu_dist --download-hypre --download-ml --download-parmetis --download-metis --download-triangle --download-chaco --download-elemental --with-debugging=0
> 
> [0]PETSC ERROR: #1 EPSSetUp_Power() line 64 in /Users/xzhao/software/slepc/slepc-3.5.4/src/eps/impls/power/power.c
> 
> [0]PETSC ERROR: #2 EPSSetUp() line 120 in /Users/xzhao/software/slepc/slepc-3.5.4/src/eps/interface/epssetup.c
> 
> [0]PETSC ERROR: #3 EPSSolve() line 88 in /Users/xzhao/software/slepc/slepc-3.5.4/src/eps/interface/epssolve.c
> 
> [0]PETSC ERROR: #4 compute_eigenvalue() line 318 in brownian_system.C
> 
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