NAG Library Manual, Mark 27.2
```    Program f11defe

!     F11DEF Example Program Text

!     Mark 27.2 Release. NAG Copyright 2021.

!     .. Use Statements ..
Use nag_library, Only: f11def, nag_wp
!     .. Implicit None Statement ..
Implicit None
!     .. Parameters ..
Integer, Parameter               :: nin = 5, nout = 6
!     .. Local Scalars ..
Real (Kind=nag_wp)               :: omega, rnorm, tol
Integer                          :: i, ifail, itn, l, lwork, m, maxitn,  &
n, nnz
Character (8)                    :: method
Character (1)                    :: precon
!     .. Local Arrays ..
Real (Kind=nag_wp), Allocatable  :: a(:), b(:), work(:), x(:)
Integer, Allocatable             :: icol(:), irow(:), iwork(:)
!     .. Intrinsic Procedures ..
Intrinsic                        :: max
!     .. Executable Statements ..
Write (nout,*) 'F11DEF Example Program Results'
Write (nout,*)
!     Skip heading in data file

l = n
If (precon=='N' .Or. precon=='n') Then
l = 0
End If
lwork = max(4*n+m*(m+n+5)+l+101,8*n+l+100,2*n*(m+3)+m*(m+2)+l+100,       &
11*n+l+100)

Allocate (a(nnz),b(n),work(lwork),x(n),icol(nnz),irow(nnz),iwork(2*n+1))

Do i = 1, nnz
End Do

!     Read right-hand side vector b and initial approximate solution x

!     Solve Ax = b using F11DEF

!     ifail: behaviour on error exit
!             =0 for hard exit, =1 for quiet-soft, =-1 for noisy-soft
ifail = 0
Call f11def(method,precon,n,nnz,a,irow,icol,omega,b,m,tol,maxitn,x,      &
rnorm,itn,work,lwork,iwork,ifail)

Write (nout,'(A,I10,A)') ' Converged in', itn, ' iterations'
Write (nout,'(A,1P,E16.3)') ' Final residual norm =', rnorm
Write (nout,*)

!     Output x

Write (nout,*) '           X'
Write (nout,'(1X,1P,E16.4)') x(1:n)

End Program f11defe
```