Date: 2021-09-20T09:44:13+00:00

Actual source code: ex23f90.F90
slepc-3.15.2 2021-09-20
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      1: !
      2: !  - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
      3: !  SLEPc - Scalable Library for Eigenvalue Problem Computations
      4: !  Copyright (c) 2002-2021, 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> ./ex23f90 [-help] [-t <t>] [-m <m>] [SLEPc opts]
     11: !
     12: !  Description: Computes exp(t*A)*v for a matrix associated with a
     13: !  Markov model. This is the Fortran90 equivalent to ex23.c
     14: !
     15: !  The command line options are:
     16: !    -t <t>, where <t> = time parameter (multiplies the matrix)
     17: !    -m <m>, where <m> = number of grid subdivisions in each dimension
     18: !
     19: ! ----------------------------------------------------------------------
     20: !
     21:       program main
     22: #include <slepc/finclude/slepcmfn.h>
     23:       use slepcmfn
     24:       implicit none

     26: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     27: !     Declarations
     28: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     29: !
     30: !  Variables:
     31: !     A      problem matrix
     32: !     mfn    matrix function solver context

     34:       Mat            A
     35:       MFN            mfn
     36:       FN             f
     37:       PetscReal      tol, norm, cst, pd, pu
     38:       PetscScalar    t, z
     39:       Vec            v, y
     40:       PetscInt       N, m, ncv, maxit, its, ii, jj
     41:       PetscInt       i, j, jmax, ix, Istart, Iend
     42:       PetscMPIInt    rank
     43:       PetscErrorCode ierr
     44:       PetscBool      flg
     45:       MFNConvergedReason reason

     47: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     48: !     Beginning of program
     49: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

     51:       call SlepcInitialize(PETSC_NULL_CHARACTER,ierr)
     52:       if (ierr .ne. 0) then
     53:         print*,'SlepcInitialize failed'
     54:         stop
     55:       endif
     56:       call MPI_Comm_rank(PETSC_COMM_WORLD,rank,ierr);CHKERRA(ierr)
     57:       m = 15
     58:       call PetscOptionsGetInt(PETSC_NULL_OPTIONS,PETSC_NULL_CHARACTER,'-m',m,flg,ierr);CHKERRA(ierr)
     59:       t = 2.0
     60:       call PetscOptionsGetScalar(PETSC_NULL_OPTIONS,PETSC_NULL_CHARACTER,'-t',t,flg,ierr);CHKERRA(ierr)
     61:       N = m*(m+1)/2
     62:       if (rank .eq. 0) then
     63:         write(*,100) N, m
     64:       endif
     65:  100  format (/'Markov y=exp(t*A)*e_1, N=',I6,' (m=',I4,')')

     67: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     68: !     Compute the transition probability matrix, A
     69: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

     71:       call MatCreate(PETSC_COMM_WORLD,A,ierr);CHKERRA(ierr)
     72:       call MatSetSizes(A,PETSC_DECIDE,PETSC_DECIDE,N,N,ierr);CHKERRA(ierr)
     73:       call MatSetFromOptions(A,ierr);CHKERRA(ierr)
     74:       call MatSetUp(A,ierr);CHKERRA(ierr)
     75:       call MatGetOwnershipRange(A,Istart,Iend,ierr);CHKERRA(ierr)
     76:       ix = 0
     77:       cst = 0.5/real(m-1)
     78:       do i=1,m
     79:         jmax = m-i+1
     80:         do j=1,jmax
     81:           ix = ix + 1
     82:           ii = ix - 1
     83:           if (ix-1.ge.Istart .and. ix.le.Iend) then
     84:             if (j.ne.jmax) then
     85:               pd = cst*(i+j-1)
     86:               !** north
     87:               if (i.eq.1) then
     88:                 z = 2.0*pd
     89:               else
     90:                 z = pd
     91:               end if
     92:               call MatSetValue(A,ii,ix,z,INSERT_VALUES,ierr);CHKERRA(ierr)
     93:               !** east
     94:               if (j.eq.1) then
     95:                 z = 2.0*pd
     96:               else
     97:                 z = pd
     98:               end if
     99:               jj = ix+jmax-1
    100:               call MatSetValue(A,ii,jj,z,INSERT_VALUES,ierr);CHKERRA(ierr)
    101:             end if

    103:             !** south
    104:             pu = 0.5 - cst*(i+j-3)
    105:             z = pu
    106:             if (j.gt.1) then
    107:               jj = ix-2
    108:               call MatSetValue(A,ii,jj,z,INSERT_VALUES,ierr);CHKERRA(ierr)
    109:             end if
    110:             !** west
    111:             if (i.gt.1) then
    112:               jj = ix-jmax-2
    113:               call MatSetValue(A,ii,jj,z,INSERT_VALUES,ierr);CHKERRA(ierr)
    114:             end if
    115:           end if
    116:         end do
    117:       end do
    118:       call MatAssemblyBegin(A,MAT_FINAL_ASSEMBLY,ierr);CHKERRA(ierr)
    119:       call MatAssemblyEnd(A,MAT_FINAL_ASSEMBLY,ierr);CHKERRA(ierr)

    121: !     ** Set v = e_1
    122:       call MatCreateVecs(A,y,v,ierr);CHKERRA(ierr)
    123:       ii = 0
    124:       z = 1.0
    125:       call VecSetValue(v,ii,z,INSERT_VALUES,ierr);CHKERRA(ierr)
    126:       call VecAssemblyBegin(v,ierr);CHKERRA(ierr)
    127:       call VecAssemblyEnd(v,ierr);CHKERRA(ierr)

    129: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    130: !     Create the solver and set various options
    131: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

    133: !     ** Create matrix function solver context
    134:       call MFNCreate(PETSC_COMM_WORLD,mfn,ierr);CHKERRA(ierr)

    136: !     ** Set operator matrix, the function to compute, and other options
    137:       call MFNSetOperator(mfn,A,ierr);CHKERRA(ierr)
    138:       call MFNGetFN(mfn,f,ierr);CHKERRA(ierr)
    139:       call FNSetType(f,FNEXP,ierr);CHKERRA(ierr)
    140:       z = 1.0
    141:       call FNSetScale(f,t,z,ierr);CHKERRA(ierr)
    142:       tol = 0.0000001
    143:       call MFNSetTolerances(mfn,tol,PETSC_DEFAULT_INTEGER,ierr);CHKERRA(ierr)

    145: !     ** Set solver parameters at runtime
    146:       call MFNSetFromOptions(mfn,ierr);CHKERRA(ierr)

    148: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    149: !     Solve the problem, y=exp(t*A)*v
    150: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

    152:       call MFNSolve(mfn,v,y,ierr);CHKERRA(ierr)
    153:       call MFNGetConvergedReason(mfn,reason,ierr);CHKERRA(ierr)
    154:       if (reason.lt.0) then; SETERRA(PETSC_COMM_WORLD,1,'Solver did not converge'); endif
    155:       call VecNorm(y,NORM_2,norm,ierr);CHKERRA(ierr)

    157: !     ** Optional: Get some information from the solver and display it
    158:       call MFNGetIterationNumber(mfn,its,ierr);CHKERRA(ierr)
    159:       if (rank .eq. 0) then
    160:         write(*,120) its
    161:       endif
    162:  120  format (' Number of iterations of the method: ',I4)
    163:       call MFNGetDimensions(mfn,ncv,ierr);CHKERRA(ierr)
    164:       if (rank .eq. 0) then
    165:         write(*,130) ncv
    166:       endif
    167:  130  format (' Subspace dimension:',I4)
    168:       call MFNGetTolerances(mfn,tol,maxit,ierr);CHKERRA(ierr)
    169:       if (rank .eq. 0) then
    170:         write(*,140) tol,maxit
    171:       endif
    172:  140  format (' Stopping condition: tol=',f10.7,' maxit=',I4)

    174: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    175: !     Display solution and clean up
    176: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

    178:       if (rank .eq. 0) then
    179:         write(*,150) PetscRealPart(t),norm
    180:       endif
    181:  150  format (' Computed vector at time t=',f4.1,' has norm ',f8.5)

    183:       call MFNDestroy(mfn,ierr);CHKERRA(ierr)
    184:       call MatDestroy(A,ierr);CHKERRA(ierr)
    185:       call VecDestroy(v,ierr);CHKERRA(ierr)
    186:       call VecDestroy(y,ierr);CHKERRA(ierr)
    187:       call SlepcFinalize(ierr)
    188:       end

    190: !/*TEST
    191: !
    192: !   test:
    193: !      suffix: 1
    194: !      args: -mfn_ncv 6
    195: !
    196: !TEST*/