Program f08kjfe

!     F08KJF Example Program Text

!     Mark 30.2 Release. NAG Copyright 2024.

!     .. Use Statements ..
      Use nag_library, Only: ddisna, dgesvj, nag_wp, x02ajf, x04caf
!     .. Implicit None Statement ..
      Implicit None
!     .. Parameters ..
      Integer, Parameter               :: nin = 5, nout = 6
!     .. Local Scalars ..
      Real (Kind=nag_wp)               :: eps, serrbd
      Integer                          :: i, ifail, info, j, lda, ldv, lwork,  &
                                          m, n
!     .. Local Arrays ..
      Real (Kind=nag_wp), Allocatable  :: a(:,:), rcondu(:), rcondv(:), s(:),  &
                                          v(:,:), work(:)
!     .. Intrinsic Procedures ..
      Intrinsic                        :: abs
!     .. Executable Statements ..
      Write (nout,*) 'F08KJF Example Program Results'
      Write (nout,*)
      Flush (nout)
!     Skip heading in data file
      Read (nin,*)
      Read (nin,*) m, n
      lda = m
      ldv = n
      lwork = n + m
      Allocate (a(lda,n),rcondu(m),rcondv(m),s(n),v(ldv,n),work(lwork))

!     Read the m by n matrix A from data file

      Read (nin,*)((a(i,j),j=1,n),i=1,m)

!     Compute the singular values and left and right singular vectors
!     of A (A = U*S*V, m.ge.n)

!     The NAG name equivalent of dgesvj is f08kjf
      Call dgesvj('G','U','V',m,n,a,lda,s,0,v,ldv,work,lwork,info)

      If (info==0) Then

!       Compute the approximate error bound for the computed singular values
!       using the 2-norm, s(1) = norm(A), and machine precision, eps.
        eps = x02ajf()
        serrbd = eps*s(1)

!       Print solution
        Write (nout,*) 'Singular values'
        Write (nout,99999)(s(j),j=1,n)

        If (abs(work(1)-1.0_nag_wp)>eps) Then
          Write (nout,99996) 'Values need scaling by factor = ', work(1)
        End If
        Flush (nout)

!       ifail: behaviour on error exit
!              =0 for hard exit, =1 for quiet-soft, =-1 for noisy-soft
        ifail = 0
        Call x04caf('General',' ',m,n,a,lda,'Left singular vectors',ifail)

        Write (nout,*)
        Flush (nout)

        ifail = 0
        Call x04caf('General',' ',n,n,v,ldv,'Right singular vectors',ifail)

!       Call DDISNA (F08FLF) to estimate reciprocal condition
!       numbers for the singular vectors
        Call ddisna('Left',m,n,s,rcondu,info)
        Call ddisna('Right',m,n,s,rcondv,info)

!       Print the approximate error bounds for the singular values
!       and vectors
        Write (nout,'(/1X,A)') 'Error estimate for the singular values'
        Write (nout,99998) serrbd
        Write (nout,'(/1X,A)') 'Error estimates for left singular vectors'
        Write (nout,99998)(serrbd/rcondu(i),i=1,n)
        Write (nout,'(/1X,A)') 'Error estimates for right singular vectors'
        Write (nout,99998)(serrbd/rcondv(i),i=1,n)
      Else
        Write (nout,99997) 'Failure in DGESVJ. INFO =', info
      End If

99999 Format (3X,(8F8.4))
99998 Format (4X,1P,6E11.1)
99997 Format (1X,A,I4)
99996 Format (/,1X,A,1P,E13.5)
    End Program f08kjfe