Program f07pdfe

!     F07PDF Example Program Text

!     Mark 29.2 Release. NAG Copyright 2023.

!     .. Use Statements ..
      Use nag_library, Only: dsptrf, nag_wp, x04ccf
!     .. Implicit None Statement ..
      Implicit None
!     .. Parameters ..
      Integer, Parameter               :: nin = 5, nout = 6
!     .. Local Scalars ..
      Integer                          :: i, ifail, info, j, n
      Character (1)                    :: uplo
!     .. Local Arrays ..
      Real (Kind=nag_wp), Allocatable  :: ap(:)
      Integer, Allocatable             :: ipiv(:)
!     .. Executable Statements ..
      Write (nout,*) 'F07PDF Example Program Results'
!     Skip heading in data file
      Read (nin,*)
      Read (nin,*) n

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

!     Read A from data file

      Read (nin,*) uplo
      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

!     Factorize A
!     The NAG name equivalent of dsptrf is f07pdf
      Call dsptrf(uplo,n,ap,ipiv,info)

      Write (nout,*)
      Flush (nout)

!     Print details of factorization

!     ifail: behaviour on error exit
!            =0 for hard exit, =1 for quiet-soft, =-1 for noisy-soft
      ifail = 0
      Call x04ccf(uplo,'Nonunit',n,ap,'Details of factorization',ifail)

!     Print pivot indices

      Write (nout,*)
      Write (nout,*) 'IPIV'
      Write (nout,99999) ipiv(1:n)

      If (info/=0) Then
        Write (nout,*) 'The factor D is singular'
      End If

99999 Format ((3X,7I11))
    End Program f07pdfe