Program f07bafe

!     F07BAF Example Program Text

!     Mark 27.3 Release. NAG Copyright 2021.

!     .. Use Statements ..
      Use nag_library, Only: dgbsv, nag_wp, x04cef
!     .. Implicit None Statement ..
      Implicit None
!     .. Parameters ..
      Integer, Parameter               :: nin = 5, nout = 6
!     .. Local Scalars ..
      Integer                          :: i, ifail, info, j, k, kl, ku, ldab,  &
                                          n
!     .. Local Arrays ..
      Real (Kind=nag_wp), Allocatable  :: ab(:,:), b(:)
      Integer, Allocatable             :: ipiv(:)
!     .. Intrinsic Procedures ..
      Intrinsic                        :: max, min
!     .. Executable Statements ..
      Write (nout,*) 'F07BAF Example Program Results'
      Write (nout,*)
!     Skip heading in data file
      Read (nin,*)
      Read (nin,*) n, kl, ku
      ldab = 2*kl + ku + 1
      Allocate (ab(ldab,n),b(n),ipiv(n))

!     Read the band matrix A and the right hand side b from data file

      k = kl + ku + 1
      Read (nin,*)((ab(k+i-j,j),j=max(i-kl,1),min(i+ku,n)),i=1,n)
      Read (nin,*) b(1:n)

!     Solve the equations Ax = b for x
!     The NAG name equivalent of dgbsv is f07baf
      Call dgbsv(n,kl,ku,1,ab,ldab,ipiv,b,n,info)

      If (info==0) Then

!       Print solution

        Write (nout,*) 'Solution'
        Write (nout,99999) b(1:n)

!       Print details of the factorization

        Write (nout,*)
        Flush (nout)

!       ifail: behaviour on error exit
!              =0 for hard exit, =1 for quiet-soft, =-1 for noisy-soft
        ifail = 0
        Call x04cef(n,n,kl,kl+ku,ab,ldab,'Details of factorization',ifail)

!       Print pivot indices'

        Write (nout,*)
        Write (nout,*) 'Pivot indices'
        Write (nout,99998) ipiv(1:n)

      Else
        Write (nout,99997) 'The (', info, ',', info, ')',                      &
          ' element of the factor U is zero'
      End If

99999 Format ((3X,7F11.4))
99998 Format ((3X,7I11))
99997 Format (1X,A,I3,A,I3,A,A)
    End Program f07bafe