NAG Library Manual, Mark 27.2
```    Program f07cnfe

!     F07CNF Example Program Text

!     Mark 27.2 Release. NAG Copyright 2021.

!     .. Use Statements ..
Use nag_library, Only: nag_wp, zgtsv
!     .. Implicit None Statement ..
Implicit None
!     .. Parameters ..
Integer, Parameter               :: nin = 5, nout = 6
!     .. Local Scalars ..
Integer                          :: info, n
!     .. Local Arrays ..
Complex (Kind=nag_wp), Allocatable :: b(:), d(:), dl(:), du(:)
!     .. Executable Statements ..
Write (nout,*) 'F07CNF Example Program Results'
Write (nout,*)
!     Skip heading in data file

Allocate (b(n),d(n),dl(n-1),du(n-1))

!     Read the tridiagonal matrix A and the right hand side B from
!     data file

!     Solve the equations Ax = b for x
!     The NAG name equivalent of zgtsv is f07cnf
Call zgtsv(n,1,dl,d,du,b,n,info)

If (info==0) Then

!       Print solution

Write (nout,*) 'Solution'
Write (nout,99999) b(1:n)

Else
Write (nout,99998) 'The (', info, ',', info, ')',                      &
' element of the factor U is zero'
End If

99999 Format (4(' (',F8.4,',',F8.4,')',:))
99998 Format (1X,A,I3,A,I3,A,A)
End Program f07cnfe
```