Program f07hgfe

!     F07HGF Example Program Text

!     Mark 30.1 Release. NAG Copyright 2024.

!     .. Use Statements ..
      Use nag_library, Only: dlansb => f06ref, dpbcon, dpbtrf, nag_wp, x02ajf
!     .. Implicit None Statement ..
      Implicit None
!     .. Parameters ..
      Integer, Parameter               :: nin = 5, nout = 6
!     .. Local Scalars ..
      Real (Kind=nag_wp)               :: anorm, rcond
      Integer                          :: i, info, j, kd, ldab, n
      Character (1)                    :: uplo
!     .. Local Arrays ..
      Real (Kind=nag_wp), Allocatable  :: ab(:,:), work(:)
      Integer, Allocatable             :: iwork(:)
!     .. Intrinsic Procedures ..
      Intrinsic                        :: max, min
!     .. Executable Statements ..
      Write (nout,*) 'F07HGF Example Program Results'
!     Skip heading in data file
      Read (nin,*)
      Read (nin,*) n, kd
      ldab = kd + 1
      Allocate (ab(ldab,n),work(3*n),iwork(n))

!     Read A from data file

      Read (nin,*) uplo
      If (uplo=='U') Then
        Do i = 1, n
          Read (nin,*)(ab(kd+1+i-j,j),j=i,min(n,i+kd))
        End Do
      Else If (uplo=='L') Then
        Do i = 1, n
          Read (nin,*)(ab(1+i-j,j),j=max(1,i-kd),i)
        End Do
      End If

!     Compute norm of A

!     f06ref is the NAG name equivalent of the LAPACK auxiliary dlansb
      anorm = dlansb('1-norm',uplo,n,kd,ab,ldab,work)

!     Factorize A
!     The NAG name equivalent of dpbtrf is f07hdf
      Call dpbtrf(uplo,n,kd,ab,ldab,info)

      Write (nout,*)
      If (info==0) Then

!       Estimate condition number
!       The NAG name equivalent of dpbcon is f07hgf
        Call dpbcon(uplo,n,kd,ab,ldab,anorm,rcond,work,iwork,info)

        If (rcond>=x02ajf()) Then
          Write (nout,99999) 'Estimate of condition number =',                 &
            1.0_nag_wp/rcond
        Else
          Write (nout,*) 'A is singular to working precision'
        End If
      Else
        Write (nout,*) 'A is not positive definite'
      End If

99999 Format (1X,A,1P,E10.2)
    End Program f07hgfe