Subversion Repositories slepc-dev

!

!  Program usage: mpirun -np n ex1f [-help] [-n <n>] [all SLEPc options]

!

!  Description: Simple example that solves an eigensystem with the EPS object.

!  The standard symmetric eigenvalue problem to be solved corresponds to the

!  Laplacian operator in 1 dimension.

!

!  The command line options are:

!    -n <n>, where <n> = number of grid points = matrix size

!

! ----------------------------------------------------------------------

!

      program main

      implicit none

#include "finclude/petsc.h"

#include "finclude/petscvec.h"

#include "finclude/petscmat.h"

#include "finclude/slepc.h"

#include "finclude/slepceps.h"

! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

!     Declarations

! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

!

!  Variables:

!     A     operator matrix

!     eps   eigenproblem solver context

      Mat          A

      EPS          eps

      EPSType      type

      PetscReal    tol, error

      PetscScalar  kr, ki

      integer      rank, n, nev, ierr, maxit, i, its, nconv

      integer      col(3), Istart, Iend

      PetscTruth   flg

      PetscScalar  value(3)

! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

!     Beginning of program

! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

      call SlepcInitialize(PETSC_NULL_CHARACTER,ierr)

      call MPI_Comm_rank(PETSC_COMM_WORLD,rank,ierr)

      n = 30

      call PetscOptionsGetInt(PETSC_NULL_CHARACTER,'-n',n,flg,ierr)

      if (rank .eq. 0) then

        write(*,100) n

      endif

 100  format (/'1-D Laplacian Eigenproblem, n =',I3)

! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

!     Compute the operator matrix that defines the eigensystem, Ax=kx

! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

      call MatCreate(PETSC_COMM_WORLD,A,ierr)

      call MatSetSizes(A,PETSC_DECIDE,PETSC_DECIDE,n,n,ierr)

      call MatSetFromOptions(A,ierr)

      call MatGetOwnershipRange(A,Istart,Iend,ierr)

      if (Istart .eq. 0) then

        i = 0

        col(1) = 0

        col(2) = 1

        value(1) =  2.0

        value(2) = -1.0

        call MatSetValues(A,1,i,2,col,value,INSERT_VALUES,ierr)

        Istart = Istart+1

      endif

      if (Iend .eq. n) then

        i = n-1

        col(1) = n-2

        col(2) = n-1

        value(1) = -1.0

        value(2) =  2.0

        call MatSetValues(A,1,i,2,col,value,INSERT_VALUES,ierr)

        Iend = Iend-1

      endif

      value(1) = -1.0

      value(2) =  2.0

      value(3) = -1.0

      do i=Istart,Iend-1

        col(1) = i-1

        col(2) = i

        col(3) = i+1

        call MatSetValues(A,1,i,3,col,value,INSERT_VALUES,ierr)

      enddo

      call MatAssemblyBegin(A,MAT_FINAL_ASSEMBLY,ierr)

      call MatAssemblyEnd(A,MAT_FINAL_ASSEMBLY,ierr)

! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

!     Create the eigensolver and display info

! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

!     ** Create eigensolver context

      call EPSCreate(PETSC_COMM_WORLD,eps,ierr)

!     ** Set operators. In this case, it is a standard eigenvalue problem

      call EPSSetOperators(eps,A,PETSC_NULL_OBJECT,ierr)

      call EPSSetProblemType(eps,EPS_HEP,ierr)

!     ** Set solver parameters at runtime

      call EPSSetFromOptions(eps,ierr)

! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

!     Solve the eigensystem

! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

      call EPSSolve(eps,ierr)

      call EPSGetIterationNumber(eps,its,ierr)

      if (rank .eq. 0) then

        write(*,110) its

      endif

 110  format (/' Number of iterations of the method:',I4)

!     ** Optional: Get some information from the solver and display it

      call EPSGetType(eps,type,ierr)

      if (rank .eq. 0) then

        write(*,120) type

      endif

 120  format (' Solution method: ',A)

      call EPSGetDimensions(eps,nev,PETSC_NULL_INTEGER,ierr)

      if (rank .eq. 0) then

        write(*,130) nev

      endif

 130  format (/' Number of requested eigenvalues:',I2)

      call EPSGetTolerances(eps,tol,maxit,ierr)

      if (rank .eq. 0) then

        write(*,140) tol, maxit

      endif

 140  format (' Stopping condition: tol=',1P,E10.4,', maxit=',I4)

! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

!     Display solution and clean up

! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

!     ** Get number of converged eigenpairs

      call EPSGetConverged(eps,nconv,ierr)

      if (rank .eq. 0) then

        write(*,150) nconv

      endif

 150  format (' Number of converged eigenpairs:',I2/)

!     ** Display eigenvalues and relative errors

      if (nconv.gt.0 .and. rank.eq.0) then

        write(*,*) '         k          ||Ax-kx||/||kx||'

        write(*,*) ' ----------------- ------------------'

        do i=0,nconv-1

!         ** Get converged eigenpairs: i-th eigenvalue is stored in kr

!         ** (real part) and ki (imaginary part)

          call EPSGetEigenpair(eps,i,kr,ki,PETSC_NULL,PETSC_NULL,ierr)

!         ** Compute the relative error associated to each eigenpair

          call EPSComputeRelativeError(eps,i,error,ierr)

          write(*,160) PetscRealPart(kr), error

 160      format (1P,'   ',E12.4,'       ',E12.4)

        enddo

        write(*,*)

      endif

!     ** Free work space

      call EPSDestroy(eps,ierr)

      call MatDestroy(A,ierr)

      call SlepcFinalize(ierr)

      end