Date: 2026-01-20T11:35:40+00:00

Actual source code: test7f.F90

      1: !
      2: !  - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
      3: !  SLEPc - Scalable Library for Eigenvalue Problem Computations
      4: !  Copyright (c) 2002-, Universitat Politecnica de Valencia, Spain
      5: !
      6: !  This file is part of SLEPc.
      7: !  SLEPc is distributed under a 2-clause BSD license (see LICENSE).
      8: !  - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
      9: !
     10: !  Program usage: mpiexec -n <np> ./test7f [-help] [-n <n>] [all SLEPc options]
     11: !
     12: !  Description: Simple example that solves an eigensystem with the EPS object.
     13: !  Same problem as ex1f but with simplified output.
     14: !
     15: !  The command line options are:
     16: !    -n <n>, where <n> = number of grid points = matrix size
     17: !
     18: ! ----------------------------------------------------------------------
     19: !
     20:       program main
     21: #include <slepc/finclude/slepceps.h>
     22:       use slepceps
     23:       implicit none

     25: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     26: !     Declarations
     27: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     28: !
     29: !  Variables:
     30: !     A     operator matrix
     31: !     eps   eigenproblem solver context

     33:       Mat            A
     34:       EPS            eps
     35:       EPSType        tname
     36:       PetscInt       n, i, Istart, Iend
     37:       PetscInt       nev, nini
     38:       PetscInt       col(3)
     39:       PetscInt       i0, i1, i2, i3
     40:       PetscMPIInt    rank
     41:       PetscErrorCode ierr
     42:       PetscBool      flg
     43:       PetscScalar    value(3), one
     44:       Vec            v(1)

     46: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     47: !     Beginning of program
     48: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

     50:       PetscCallA(SlepcInitialize(PETSC_NULL_CHARACTER,ierr))
     51:       PetscCallMPIA(MPI_Comm_rank(PETSC_COMM_WORLD,rank,ierr))
     52:       n = 30
     53:       PetscCallA(PetscOptionsGetInt(PETSC_NULL_OPTIONS,PETSC_NULL_CHARACTER,'-n',n,flg,ierr))

     55:       if (rank .eq. 0) then
     56:         write(*,100) n
     57:       endif
     58:  100  format (/'1-D Laplacian Eigenproblem, n =',I3,' (Fortran)')

     60: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     61: !     Compute the operator matrix that defines the eigensystem, Ax=kx
     62: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

     64:       PetscCallA(MatCreate(PETSC_COMM_WORLD,A,ierr))
     65:       PetscCallA(MatSetSizes(A,PETSC_DECIDE,PETSC_DECIDE,n,n,ierr))
     66:       PetscCallA(MatSetFromOptions(A,ierr))

     68:       i0 = 0
     69:       i1 = 1
     70:       i2 = 2
     71:       i3 = 3
     72:       PetscCallA(MatGetOwnershipRange(A,Istart,Iend,ierr))
     73:       if (Istart .eq. 0) then
     74:         i = 0
     75:         col(1) = 0
     76:         col(2) = 1
     77:         value(1) =  2.0
     78:         value(2) = -1.0
     79:         PetscCallA(MatSetValues(A,i1,[i],i2,col,value,INSERT_VALUES,ierr))
     80:         Istart = Istart+1
     81:       endif
     82:       if (Iend .eq. n) then
     83:         i = n-1
     84:         col(1) = n-2
     85:         col(2) = n-1
     86:         value(1) = -1.0
     87:         value(2) =  2.0
     88:         PetscCallA(MatSetValues(A,i1,[i],i2,col,value,INSERT_VALUES,ierr))
     89:         Iend = Iend-1
     90:       endif
     91:       value(1) = -1.0
     92:       value(2) =  2.0
     93:       value(3) = -1.0
     94:       do i=Istart,Iend-1
     95:         col(1) = i-1
     96:         col(2) = i
     97:         col(3) = i+1
     98:         PetscCallA(MatSetValues(A,i1,[i],i3,col,value,INSERT_VALUES,ierr))
     99:       enddo

    101:       PetscCallA(MatAssemblyBegin(A,MAT_FINAL_ASSEMBLY,ierr))
    102:       PetscCallA(MatAssemblyEnd(A,MAT_FINAL_ASSEMBLY,ierr))

    104:       PetscCallA(MatCreateVecs(A,v(1),PETSC_NULL_VEC,ierr))
    105:       one = 1.0
    106:       if (Istart .eq. 0) then
    107:         PetscCallA(VecSetValue(v(1),i0,one,INSERT_VALUES,ierr))
    108:       endif
    109:       PetscCallA(VecAssemblyBegin(v(1),ierr))
    110:       PetscCallA(VecAssemblyEnd(v(1),ierr))

    112: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    113: !     Create the eigensolver and display info
    114: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

    116: !     ** Create eigensolver context
    117:       PetscCallA(EPSCreate(PETSC_COMM_WORLD,eps,ierr))

    119: !     ** Set operators. In this case, it is a standard eigenvalue problem
    120:       PetscCallA(EPSSetOperators(eps,A,PETSC_NULL_MAT,ierr))
    121:       PetscCallA(EPSSetProblemType(eps,EPS_HEP,ierr))

    123: !     ** Set solver parameters at runtime
    124:       PetscCallA(EPSSetFromOptions(eps,ierr))

    126: !     ** Set initial vectors
    127:       nini = 1
    128:       PetscCallA(EPSSetInitialSpace(eps,nini,v,ierr))

    130: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    131: !     Solve the eigensystem
    132: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

    134:       PetscCallA(EPSSolve(eps,ierr))

    136: !     ** Optional: Get some information from the solver and display it
    137:       PetscCallA(EPSGetType(eps,tname,ierr))
    138:       if (rank .eq. 0) then
    139:         write(*,120) tname
    140:       endif
    141:  120  format (' Solution method: ',A)
    142:       PetscCallA(EPSGetDimensions(eps,nev,PETSC_NULL_INTEGER,PETSC_NULL_INTEGER,ierr))
    143:       if (rank .eq. 0) then
    144:         write(*,130) nev
    145:       endif
    146:  130  format (' Number of requested eigenvalues:',I2)

    148: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    149: !     Display solution and clean up
    150: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

    152:       PetscCallA(EPSErrorView(eps,EPS_ERROR_RELATIVE,PETSC_NULL_VIEWER,ierr))
    153:       PetscCallA(EPSDestroy(eps,ierr))
    154:       PetscCallA(MatDestroy(A,ierr))
    155:       PetscCallA(VecDestroy(v(1),ierr))

    157:       PetscCallA(SlepcFinalize(ierr))
    158:       end

    160: !/*TEST
    161: !
    162: !   test:
    163: !      suffix: 1
    164: !      args: -eps_nev 4 -eps_ncv 19
    165: !      filter: sed -e "s/83791/83792/"
    166: !
    167: !TEST*/