Program f07fffe

!     F07FFF Example Program Text

!     Mark 28.3 Release. NAG Copyright 2022.

!     .. Use Statements ..
      Use nag_library, Only: dpoequ, dscal, f06fcf, nag_wp, x02ajf, x02amf,    &
                             x02bhf, x04caf
!     .. Implicit None Statement ..
      Implicit None
!     .. Parameters ..
      Real (Kind=nag_wp), Parameter    :: one = 1.0_nag_wp
      Real (Kind=nag_wp), Parameter    :: thresh = 0.1_nag_wp
      Integer, Parameter               :: nin = 5, nout = 6
!     .. Local Scalars ..
      Real (Kind=nag_wp)               :: amax, big, scond, small
      Integer                          :: i, ifail, info, j, lda, n
!     .. Local Arrays ..
      Real (Kind=nag_wp), Allocatable  :: a(:,:), s(:)
!     .. Intrinsic Procedures ..
      Intrinsic                        :: real
!     .. Executable Statements ..
      Write (nout,*) 'F07FFF Example Program Results'
      Write (nout,*)
      Flush (nout)
!     Skip heading in data file
      Read (nin,*)
      Read (nin,*) n
      lda = n
      Allocate (a(lda,n),s(n))

!     Read the upper triangular part of the matrix A from data file

      Read (nin,*)(a(i,i:n),i=1,n)

!     Print the matrix A

!     ifail: behaviour on error exit
!             =0 for hard exit, =1 for quiet-soft, =-1 for noisy-soft
      ifail = 0
      Call x04caf('Upper','Non-unit',n,n,a,lda,'Matrix A',ifail)

      Write (nout,*)

!     Compute diagonal scaling factors
!     The NAG name equivalent of dpoequ is f07fff
      Call dpoequ(n,a,lda,s,scond,amax,info)

      If (info>0) Then
        Write (nout,99999) 'Diagonal element', info, ' of A is non positive'
      Else

!       Print SCOND, AMAX and the scale factors

        Write (nout,99998) 'SCOND =', scond, ', AMAX =', amax
        Write (nout,*)
        Write (nout,*) 'Diagonal scaling factors'
        Write (nout,99997) s(1:n)
        Write (nout,*)
        Flush (nout)

!       Compute values close to underflow and overflow

        small = x02amf()/(x02ajf()*real(x02bhf(),kind=nag_wp))
        big = one/small
        If ((scond<thresh) .Or. (amax<small) .Or. (amax>big)) Then

!         Scale A
!         The NAG name equivalent of dscal is f06edf
          Do j = 1, n
            Call dscal(j,s(j),a(1,j),1)
            Call f06fcf(j,s,1,a(1,j),1)
          End Do

!         Print the scaled matrix

          ifail = 0
          Call x04caf('Upper','Non-unit',n,n,a,lda,'Scaled matrix',ifail)

        End If
      End If

99999 Format (1X,A,I4,A)
99998 Format (1X,2(A,1P,E8.1))
99997 Format ((1X,1P,7E11.1))
    End Program f07fffe