Program f07gffe

!     F07GFF Example Program Text

!     Mark 30.1 Release. NAG Copyright 2024.

!     .. Use Statements ..
      Use nag_library, Only: dppequ, dscal, f06fcf, nag_wp, x02ajf, x02amf,    &
                             x02bhf, x04ccf
!     .. 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
      Character (1), Parameter         :: uplo = 'U'
!     .. Local Scalars ..
      Real (Kind=nag_wp)               :: amax, big, scond, small
      Integer                          :: i, ifail, info, j, jinc, jj, n
!     .. Local Arrays ..
      Real (Kind=nag_wp), Allocatable  :: ap(:), s(:)
!     .. Intrinsic Procedures ..
      Intrinsic                        :: real
!     .. Executable Statements ..
      Write (nout,*) 'F07GFF Example Program Results'
      Write (nout,*)
      Flush (nout)
!     Skip heading in data file
      Read (nin,*)
      Read (nin,*) n

      Allocate (ap((n*(n+1))/2),s(n))

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

      If (uplo=='U') Then
        Read (nin,*)((ap(i+(j*(j-1))/2),j=i,n),i=1,n)
      Else If (uplo=='L') Then
        Read (nin,*)((ap(i+((2*n-j)*(j-1))/2),j=1,i),i=1,n)
      End If

!     Print the matrix A

!     ifail: behaviour on error exit
!             =0 for hard exit, =1 for quiet-soft, =-1 for noisy-soft
      ifail = 0
      Call x04ccf(uplo,'Non-unit diagonal',n,ap,'Matrix A',ifail)

      Write (nout,*)

!     Compute diagonal scaling factors
!     The NAG name equivalent of dppequ is f07gff
      Call dppequ(uplo,n,ap,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

          If (uplo=='U') Then
!           The NAG name equivalent of dscal is f06edf
            jj = 1
            Do j = 1, n
              Call dscal(j,s(j),ap(jj),1)
              Call f06fcf(j,s,1,ap(jj),1)
              jj = jj + j
            End Do
          Else If (uplo=='L') Then
            jj = 1
            jinc = n
            Do j = 1, n
              Call dscal(jinc,s(j),ap(jj),1)
              Call f06fcf(jinc,s(j),1,ap(jj),1)
              jj = jj + jinc
              jinc = jinc - 1
            End Do
          End If

!         Print the scaled matrix

          ifail = 0
          Call x04ccf(uplo,'Non-unit diagonal',n,ap,'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 f07gffe