NAG Library Manual, Mark 28.7
```    Program f11dqfe

!     F11DQF Example Program Text

!     Mark 28.7 Release. NAG Copyright 2022.

!     .. Use Statements ..
Use nag_library, Only: f11dnf, f11dqf, nag_wp
!     .. Implicit None Statement ..
Implicit None
!     .. Parameters ..
Integer, Parameter               :: nin = 5, nout = 6
!     .. Local Scalars ..
Real (Kind=nag_wp)               :: dtol, rnorm, tol
Integer                          :: i, ifail, itn, la, lfill, liwork,    &
lwork, m, maxitn, n, nnz, nnzc,      &
npivm
Character (8)                    :: method
Character (1)                    :: milu, pstrat
!     .. Local Arrays ..
Complex (Kind=nag_wp), Allocatable :: a(:), b(:), work(:), x(:)
Integer, Allocatable             :: icol(:), idiag(:), ipivp(:),         &
ipivq(:), irow(:), istr(:), iwork(:)
!     .. Intrinsic Procedures ..
Intrinsic                        :: max
!     .. Executable Statements ..
Write (nout,*) 'F11DQF Example Program Results'
Write (nout,*)
!     Skip heading in data file

la = 2*nnz
liwork = 7*n + 2
lwork = max(4*n+m*(m+n+5)+121,8*n+120,2*n*(m+3)+m*(m+2)+120,11*n+120)

Allocate (a(la),b(n),work(lwork),x(n),icol(la),idiag(n),ipivp(n),        &
ipivq(n),irow(la),istr(n+1),iwork(liwork))

Do i = 1, nnz
End Do

!     Read rhs vector b and initial approximate solution x

!     Calculate incomplete LU factorization

!     ifail: behaviour on error exit
!             =0 for hard exit, =1 for quiet-soft, =-1 for noisy-soft
ifail = 0
Call f11dnf(n,nnz,a,la,irow,icol,lfill,dtol,pstrat,milu,ipivp,ipivq,     &
istr,idiag,nnzc,npivm,iwork,liwork,ifail)

!     Solve Ax = b using F11DQF

ifail = 0
Call f11dqf(method,n,nnz,a,la,irow,icol,ipivp,ipivq,istr,idiag,b,m,tol,  &
maxitn,x,rnorm,itn,work,lwork,ifail)

Write (nout,99999) itn
Write (nout,99998) rnorm
Write (nout,*)

!     Output x

Write (nout,*) '                   X'
Write (nout,99997) x(1:n)

99999 Format (1X,'Converged in',I10,' iterations')
99998 Format (1X,'Final residual norm =',1P,E16.3)
99997 Format (1X,'(',1P,E16.4,',',1P,E16.4,')')
End Program f11dqfe
```