Program f08nefe

!     F08NEF Example Program Text

!     Mark 30.1 Release. NAG Copyright 2024.

!     .. Use Statements ..
      Use nag_library, Only: dgehrd, nag_wp, x04caf
!     .. Implicit None Statement ..
      Implicit None
!     .. Parameters ..
      Real (Kind=nag_wp), Parameter    :: zero = 0.0E0_nag_wp
      Integer, Parameter               :: nin = 5, nout = 6
!     .. Local Scalars ..
      Integer                          :: i, ifail, info, lda, lwork, n
!     .. Local Arrays ..
      Real (Kind=nag_wp), Allocatable  :: a(:,:), tau(:), work(:)
!     .. Executable Statements ..
      Write (nout,*) 'F08NEF Example Program Results'
!     Skip heading in data file
      Read (nin,*)
      Read (nin,*) n
      lda = n
      lwork = 64*n
      Allocate (a(lda,n),tau(n-1),work(lwork))

!     Read A from data file

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

!     Reduce A to upper Hessenberg form

!     The NAG name equivalent of dgehrd is f08nef
      Call dgehrd(n,1,n,a,lda,tau,work,lwork,info)

!     Set the elements below the first subdiagonal to zero

      Do i = 1, n - 2
        a(i+2:n,i) = zero
      End Do

!     Print upper Hessenberg form

      Write (nout,*)
      Flush (nout)

!     ifail: behaviour on error exit
!             =0 for hard exit, =1 for quiet-soft, =-1 for noisy-soft
      ifail = 0
      Call x04caf('General',' ',n,n,a,lda,'Upper Hessenberg form',ifail)

    End Program f08nefe