NAG Library Manual, Mark 27.2
```    Program f07brfe

!     F07BRF Example Program Text

!     Mark 27.2 Release. NAG Copyright 2021.

!     .. Use Statements ..
Use nag_library, Only: nag_wp, x04dff, zgbtrf
!     .. Implicit None Statement ..
Implicit None
!     .. Parameters ..
Integer, Parameter               :: nin = 5, nout = 6
!     .. Local Scalars ..
Integer                          :: i, ifail, info, j, k, kl, ku, ldab,  &
m, n
!     .. Local Arrays ..
Complex (Kind=nag_wp), Allocatable :: ab(:,:)
Integer, Allocatable             :: ipiv(:)
Character (1)                    :: clabs(1), rlabs(1)
!     .. Intrinsic Procedures ..
Intrinsic                        :: max, min
!     .. Executable Statements ..
Write (nout,*) 'F07BRF Example Program Results'
!     Skip heading in data file
Read (nin,*) m, n, kl, ku
ldab = 2*kl + ku + 1
Allocate (ab(ldab,n),ipiv(n))

!     Read A from data file

k = kl + ku + 1

!     Factorize A
!     The NAG name equivalent of zgbtrf is f07brf
Call zgbtrf(m,n,kl,ku,ab,ldab,ipiv,info)

!     Print details of 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 x04dff(m,n,kl,kl+ku,ab,ldab,'Bracketed','F7.4',                     &
'Details of factorization','Integer',rlabs,'Integer',clabs,80,0,ifail)

!     Print pivot indices

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

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

99999 Format ((1X,I12,3I18))
End Program f07brfe
```