Date: 2023-09-05T10:18:44+00:00

Actual source code: ex15f.F
slepc-3.19.2 2023-09-05
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      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> ./ex15f [-help] [-n <n>] [-mu <mu>] [all SLEPc options]
     11: !
     12: !  Description: Singular value decomposition of the Lauchli matrix.
     13: !
     14: !  The command line options are:
     15: !    -n <n>, where <n> = matrix dimension.
     16: !    -mu <mu>, where <mu> = subdiagonal value.
     17: !
     18: ! ----------------------------------------------------------------------
     19: !
     20:       program main
     21: #include <slepc/finclude/slepcsvd.h>
     22:       use slepcsvd
     23:       implicit none

     25: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     26: !     Declarations
     27: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     28: !
     29: !  Variables:
     30: !     A     operator matrix
     31: !     svd   singular value solver context

     33:       Mat            A
     34:       SVD            svd
     35:       SVDType        tname
     36:       PetscReal      tol, error, sigma, mu
     37:       PetscInt       n, i, j, Istart, Iend
     38:       PetscInt       nsv, maxit, its, nconv
     39:       PetscMPIInt    rank
     40:       PetscErrorCode ierr
     41:       PetscBool      flg
     42:       PetscScalar    one, alpha

     44: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     45: !     Beginning of program
     46: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

     48:       call SlepcInitialize(PETSC_NULL_CHARACTER,ierr)
     49:       call MPI_Comm_rank(PETSC_COMM_WORLD,rank,ierr)
     50:       n = 100
     51:       call PetscOptionsGetInt(PETSC_NULL_OPTIONS,PETSC_NULL_CHARACTER,  &
     52:      &                        '-n',n,flg,ierr)
     53:       mu = PETSC_SQRT_MACHINE_EPSILON
     54:       call PetscOptionsGetReal(PETSC_NULL_OPTIONS,PETSC_NULL_CHARACTER, &
     55:      &                        '-mu',mu,flg,ierr)

     57:       if (rank .eq. 0) then
     58:         write(*,100) n, mu
     59:       endif
     60:  100  format (/'Lauchli SVD, n =',I3,', mu=',E12.4,' (Fortran)')

     62: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     63: !     Build the Lauchli matrix
     64: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

     66:       call MatCreate(PETSC_COMM_WORLD,A,ierr)
     67:       call MatSetSizes(A,PETSC_DECIDE,PETSC_DECIDE,n+1,n,ierr)
     68:       call MatSetFromOptions(A,ierr)
     69:       call MatSetUp(A,ierr)

     71:       call MatGetOwnershipRange(A,Istart,Iend,ierr)
     72:       one = 1.0
     73:       do i=Istart,Iend-1
     74:         if (i .eq. 0) then
     75:           do j=0,n-1
     76:             call MatSetValue(A,i,j,one,INSERT_VALUES,ierr)
     77:           end do
     78:         else
     79:           alpha = mu
     80:           call MatSetValue(A,i,i-1,alpha,INSERT_VALUES,ierr)
     81:         end if
     82:       enddo

     84:       call MatAssemblyBegin(A,MAT_FINAL_ASSEMBLY,ierr)
     85:       call MatAssemblyEnd(A,MAT_FINAL_ASSEMBLY,ierr)

     87: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     88: !     Create the singular value solver and display info
     89: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

     91: !     ** Create singular value solver context
     92:       call SVDCreate(PETSC_COMM_WORLD,svd,ierr)

     94: !     ** Set operators and problem type
     95:       call SVDSetOperators(svd,A,PETSC_NULL_MAT,ierr)
     96:       call SVDSetProblemType(svd,SVD_STANDARD,ierr)

     98: !     ** Use thick-restart Lanczos as default solver
     99:       call SVDSetType(svd,SVDTRLANCZOS,ierr)

    101: !     ** Set solver parameters at runtime
    102:       call SVDSetFromOptions(svd,ierr)

    104: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    105: !     Solve the singular value system
    106: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

    108:       call SVDSolve(svd,ierr)
    109:       call SVDGetIterationNumber(svd,its,ierr)
    110:       if (rank .eq. 0) then
    111:         write(*,110) its
    112:       endif
    113:  110  format (/' Number of iterations of the method:',I4)

    115: !     ** Optional: Get some information from the solver and display it
    116:       call SVDGetType(svd,tname,ierr)
    117:       if (rank .eq. 0) then
    118:         write(*,120) tname
    119:       endif
    120:  120  format (' Solution method: ',A)
    121:       call SVDGetDimensions(svd,nsv,PETSC_NULL_INTEGER,                 &
    122:      &                      PETSC_NULL_INTEGER,ierr)
    123:       if (rank .eq. 0) then
    124:         write(*,130) nsv
    125:       endif
    126:  130  format (' Number of requested singular values:',I2)
    127:       call SVDGetTolerances(svd,tol,maxit,ierr)
    128:       if (rank .eq. 0) then
    129:         write(*,140) tol, maxit
    130:       endif
    131:  140  format (' Stopping condition: tol=',1P,E11.4,', maxit=',I4)

    133: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    134: !     Display solution and clean up
    135: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

    137: !     ** Get number of converged singular triplets
    138:       call SVDGetConverged(svd,nconv,ierr)
    139:       if (rank .eq. 0) then
    140:         write(*,150) nconv
    141:       endif
    142:  150  format (' Number of converged approximate singular triplets:',I2/)

    144: !     ** Display singular values and relative errors
    145:       if (nconv.gt.0) then
    146:         if (rank .eq. 0) then
    147:           write(*,*) '       sigma          relative error'
    148:           write(*,*) ' ----------------- ------------------'
    149:         endif
    150:         do i=0,nconv-1
    151: !         ** Get i-th singular value
    152:           call SVDGetSingularTriplet(svd,i,sigma,PETSC_NULL_VEC,        &
    153:      &         PETSC_NULL_VEC,ierr)

    155: !         ** Compute the relative error for each singular triplet
    156:           call SVDComputeError(svd,i,SVD_ERROR_RELATIVE,error,ierr)
    157:           if (rank .eq. 0) then
    158:             write(*,160) sigma, error
    159:           endif
    160:  160      format (1P,'   ',E12.4,'       ',E12.4)

    162:         enddo
    163:         if (rank .eq. 0) then
    164:           write(*,*)
    165:         endif
    166:       endif

    168: !     ** Free work space
    169:       call SVDDestroy(svd,ierr)
    170:       call MatDestroy(A,ierr)

    172:       call SlepcFinalize(ierr)
    173:       end

    175: !/*TEST
    176: !
    177: !   test:
    178: !      suffix: 1
    179: !      filter: sed -e "s/[0-9]\.[0-9]*E[+-]\([0-9]*\)/removed/g"
    180: !
    181: !TEST*/