NAG Library Manual, Mark 27.2
```    Program f11bf_p0w_fe

!     F11BF_P0W_F Example Program Text
!     Mark 27.2 Release. NAG Copyright 2021.

!     .. Use Statements ..
Use iso_c_binding, Only: c_ptr
Use nagad_library, Only: f11bd_p0w_f, f11be_p0w_f, f11bf_p0w_f
Use nag_library, Only: nag_wp
!     .. Implicit None Statement ..
Implicit None
!     .. Parameters ..
Integer, Parameter               :: nin = 5, nout = 6
!     .. Local Scalars ..
Real (Kind=nag_wp)               :: a, alpha, anorm, b1, bb, c, sigmax,  &
stplhs, stprhs, tol
Integer                          :: i, ifail, irevcm, iterm, itn, lwork, &
lwreq, m, maxitn, monit, n
!     .. Local Arrays ..
Real (Kind=nag_wp), Allocatable  :: b(:), work(:), x(:)
Real (Kind=nag_wp)               :: wgt(1)
!     .. Intrinsic Procedures ..
Intrinsic                        :: real
!     .. Executable Statements ..
Write (nout,*) 'F11BF_P0W_F Example Program Results'
!     Skip heading in data file

lwork = 2*m*n + 1000
Allocate (b(n),x(n),work(lwork))

ifail = 0
b1 = 12.0_nag_wp
a = 1.0_nag_wp
bb = b1 - 2.0_nag_wp
c = 1.0_nag_wp

Do i = 1, n
b(i) = b1*real(i,kind=nag_wp)
End Do
b(n) = b(n) - real(n+1,kind=nag_wp)

b(1) = b(1) + (b1-1.0_nag_wp)*alpha
b(2:n-1) = b(2:n-1) + b1*alpha
b(n) = b(n) + (b1-1.0_nag_wp)*alpha

Do i = 1, n
x(1:n) = 3.0_nag_wp
End Do

!     Call F11BDF to initialize the solver
iterm = 2
maxitn = 800
anorm = 0.0_nag_wp
sigmax = 0.0_nag_wp
tol = 1.0E-10_nag_wp
monit = 0

ifail = 0
anorm,sigmax,monit,lwreq,work,lwork,ifail)

irevcm = 0
lwreq = lwork

ifail = 1
loop: Do
If (irevcm/=4) Then
ifail = -1
Select Case (irevcm)
Case (-1)
!           b = A^Tx
b(1) = bb*x(1) + a*x(2)
Do i = 2, n - 1
b(i) = c*x(i-1) + bb*x(i) + a*x(i+1)
End Do
b(n) = c*x(n-1) + bb*x(n)
Case (1)
!           b = Ax
b(1) = bb*x(1) + c*x(2)
Do i = 2, n - 1
b(i) = a*x(i-1) + bb*x(i) + c*x(i+1)
End Do
b(n) = a*x(n-1) + bb*x(n)
Case (2)
b(1:n) = x(1:n)/bb
End Select
Else If (ifail/=0) Then
Write (nout,99997) ifail
Go To 100
Else
Exit loop
End If
End Do loop

!     Obtain information about the computation

ifail = 0
ifail)

!     Print the output data

Write (nout,99996)
Write (nout,99995) 'Number of iterations for convergence:    ', itn
Write (nout,99994) 'Residual norm:                           ', stplhs
Write (nout,99994) 'Right-hand side of termination criterion:', stprhs
!     For iterm=2 anorm is not calculated

!     Output x
Write (nout,99999)
Write (nout,99998)(x(i),b(i),i=1,n)
100   Continue
99999 Format (/,2X,'  Solution vector',2X,' Residual vector')
99998 Format (1X,1P,E16.4,1X,E16.4)
99997 Format (1X,/,1X,' ** F11BE_a1W_F returned with IFAIL = ',I5)
99996 Format (/,1X,'Final Results')
99995 Format (1X,A,I4)
99994 Format (1X,A,1P,E14.4)

End Program f11bf_p0w_fe
```