Program f08ktfe

!     F08KTF Example Program Text

!     Mark 27.3 Release. NAG Copyright 2021.

!     .. Use Statements ..
      Use nag_library, Only: f06tff, nag_wp, x04dbf, zbdsqr, zgebrd, zungbr
!     .. Implicit None Statement ..
      Implicit None
!     .. Parameters ..
      Integer, Parameter               :: nin = 5, nout = 6
!     .. Local Scalars ..
      Integer                          :: i, ic, ifail, info, lda, ldc, ldu,   &
                                          ldvt, lwork, m, n
!     .. Local Arrays ..
      Complex (Kind=nag_wp), Allocatable :: a(:,:), c(:,:), taup(:), tauq(:),  &
                                          u(:,:), vt(:,:), work(:)
      Real (Kind=nag_wp), Allocatable  :: d(:), e(:), rwork(:)
      Character (1)                    :: clabs(1), rlabs(1)
!     .. Executable Statements ..
      Write (nout,*) 'F08KTF Example Program Results'
!     Skip heading in data file
      Read (nin,*)
      Do ic = 1, 2
        Read (nin,*) m, n
        lda = m
        ldc = n
        ldu = m
        ldvt = n
        lwork = 64*(m+n)
        Allocate (a(lda,n),c(ldc,n),taup(n),tauq(n),u(ldu,n),vt(ldvt,n),       &
          work(lwork),d(n),e(n-1),rwork(4*n-4))

!       Read A from data file
        Read (nin,*)(a(i,1:n),i=1,m)

!       Reduce A to bidiagonal form
!       The NAG name equivalent of zgebrd is f08ksf
        Call zgebrd(m,n,a,lda,d,e,tauq,taup,work,lwork,info)

        If (m>=n) Then

!         Copy A to VT and U
          Call f06tff('Upper',n,n,a,lda,vt,ldvt)
          Call f06tff('Lower',m,n,a,lda,u,ldu)

!         Form P**H explicitly, storing the result in VT
!         The NAG name equivalent of zungbr is f08ktf
          Call zungbr('P',n,n,m,vt,ldvt,taup,work,lwork,info)

!         Form Q explicitly, storing the result in U
          Call zungbr('Q',m,n,n,u,ldu,tauq,work,lwork,info)

!         Compute the SVD of A
!         The NAG name equivalent of zbdsqr is f08msf
          Call zbdsqr('Upper',n,n,m,0,d,e,vt,ldvt,u,ldu,c,ldc,rwork,info)

!         Print singular values, left & right singular vectors

          Write (nout,*)
          Write (nout,*) 'Example 1: singular values'
          Write (nout,99999) d(1:n)
          Write (nout,*)
          Flush (nout)

!         ifail: behaviour on error exit
!                =0 for hard exit, =1 for quiet-soft, =-1 for noisy-soft
          ifail = 0
          Call x04dbf('General',' ',n,n,vt,ldvt,'Bracketed','F7.4',            &
            'Example 1: right singular vectors, by row','Integer',rlabs,       &
            'Integer',clabs,80,0,ifail)

          Write (nout,*)
          Flush (nout)

          Call x04dbf('General',' ',m,n,u,ldu,'Bracketed','F7.4',              &
            'Example 1: left singular vectors, by column','Integer',rlabs,     &
            'Integer',clabs,80,0,ifail)

        Else

!         Copy A to VT and U
          Call f06tff('Upper',m,n,a,lda,vt,ldvt)
          Call f06tff('Lower',m,m,a,lda,u,ldu)

!         Form P**H explicitly, storing the result in VT
!         The NAG name equivalent of zungbr is f08ktf
          Call zungbr('P',m,n,m,vt,ldvt,taup,work,lwork,info)

!         Form Q explicitly, storing the result in U
          Call zungbr('Q',m,m,n,u,ldu,tauq,work,lwork,info)

!         Compute the SVD of A
!         The NAG name equivalent of zbdsqr is f08msf
          Call zbdsqr('Lower',m,n,m,0,d,e,vt,ldvt,u,ldu,c,ldc,rwork,info)

!         Print singular values, left & right singular vectors

          Write (nout,*)
          Write (nout,*) 'Example 2: singular values'
          Write (nout,99999) d(1:m)
          Write (nout,*)
          Flush (nout)

          ifail = 0
          Call x04dbf('General',' ',m,n,vt,ldvt,'Bracketed','F7.4',            &
            'Example 2: right singular vectors, by row','Integer',rlabs,       &
            'Integer',clabs,80,0,ifail)

          Write (nout,*)
          Flush (nout)

          Call x04dbf('General',' ',m,m,u,ldu,'Bracketed','F7.4',              &
            'Example 2: left singular vectors, by column','Integer',rlabs,     &
            'Integer',clabs,80,0,ifail)

        End If
        Deallocate (a,c,taup,tauq,u,vt,work,d,e,rwork)
      End Do

99999 Format (8X,4(F7.4,11X,:))
    End Program f08ktfe