NAG Library Manual, Mark 27.2
Interfaces:  FL   CL   CPP   AD
```    Program f04cffe

!     F04CFF Example Program Text

!     Mark 27.2 Release. NAG Copyright 2021.

!     .. Use Statements ..
Use nag_library, Only: f04cff, nag_wp, x04dbf
!     .. Implicit None Statement ..
Implicit None
!     .. Parameters ..
Integer, Parameter               :: nin = 5, nout = 6
Character (1), Parameter         :: uplo = 'U'
!     .. Local Scalars ..
Real (Kind=nag_wp)               :: errbnd, rcond
Integer                          :: i, ierr, ifail, j, kd, ldab, ldb, n, &
nrhs
!     .. Local Arrays ..
Complex (Kind=nag_wp), Allocatable :: ab(:,:), b(:,:)
Character (1)                    :: clabs(1), rlabs(1)
!     .. Intrinsic Procedures ..
Intrinsic                        :: max, min
!     .. Executable Statements ..
Write (nout,*) 'F04CFF Example Program Results'
Write (nout,*)
Flush (nout)
!     Skip heading in data file
Read (nin,*) n, kd, nrhs
ldab = kd + 1
ldb = n
Allocate (ab(ldab,n),b(ldb,nrhs))
!     Read the upper or lower triangular part of the band matrix A
!     from data file
If (uplo=='U') Then
Do i = 1, n
End Do
Else If (uplo=='L') Then
Do i = 1, n
End Do
End If

!     Read B from data file

!     Solve the equations AX = B for X

!     ifail: behaviour on error exit
!            =0 for hard exit, =1 for quiet-soft, =-1 for noisy-soft
ifail = 1
Call f04cff(uplo,n,kd,nrhs,ab,ldab,b,ldb,rcond,errbnd,ifail)

If (ifail==0) Then
!       Print solution, estimate of condition number and approximate
!       error bound

ierr = 0
Call x04dbf('General',' ',n,nrhs,b,ldb,'Bracketed','F7.4','Solution',  &
'Integer',rlabs,'Integer',clabs,80,0,ierr)

Write (nout,*)
Write (nout,*) 'Estimate of condition number'
Write (nout,99999) 1.0E0_nag_wp/rcond
Write (nout,*)
Write (nout,*) 'Estimate of error bound for computed solutions'
Write (nout,99999) errbnd
Else If (ifail==n+1) Then
!       Matrix A is numerically singular.  Print estimate of
!       reciprocal of condition number and solution
Write (nout,*)
Write (nout,*) 'Estimate of reciprocal of condition number'
Write (nout,99999) rcond
Write (nout,*)
Flush (nout)

ierr = 0
Call x04dbf('General',' ',n,nrhs,b,ldb,'Bracketed','F7.4','Solution',  &
'Integer',rlabs,'Integer',clabs,80,0,ierr)

Else If (ifail>0 .And. ifail<=n) Then
!       The matrix A is not positive definite to working precision
Write (nout,99998) 'The leading minor of order ', ifail,               &
' is not positive definite'
Else
Write (nout,99997) ifail
End If

99999 Format (4X,1P,E9.1)
99998 Format (1X,A,I3,A)
99997 Format (1X,' ** F04CFF returned with IFAIL = ',I5)
End Program f04cffe
```