NAG Library Manual, Mark 28.5
```    Program f07cefe

!     F07CEF Example Program Text

!     Mark 28.5 Release. NAG Copyright 2022.

!     .. Use Statements ..
Use nag_library, Only: dgttrf, dgttrs, nag_wp, x04caf
!     .. Implicit None Statement ..
Implicit None
!     .. Parameters ..
Integer, Parameter               :: nin = 5, nout = 6
!     .. Local Scalars ..
Integer                          :: i, ifail, info, ldb, n, nrhs
!     .. Local Arrays ..
Real (Kind=nag_wp), Allocatable  :: b(:,:), d(:), dl(:), du(:), du2(:)
Integer, Allocatable             :: ipiv(:)
!     .. Executable Statements ..
Write (nout,*) 'F07CEF Example Program Results'
Write (nout,*)
Flush (nout)
!     Skip heading in data file
ldb = n
Allocate (b(ldb,nrhs),d(n),dl(n-1),du(n-1),du2(n-2),ipiv(n))

!     Read the tridiagonal matrix A from data file

!     Read the right hand matrix B

!     Factorize the tridiagonal matrix A
!     The NAG name equivalent of dgttrf is f07cdf
Call dgttrf(n,dl,d,du,du2,ipiv,info)

If (info==0) Then

!       Solve the equations AX = B
!       The NAG name equivalent of dgttrs is f07cef
Call dgttrs('No transpose',n,nrhs,dl,d,du,du2,ipiv,b,ldb,info)

!       Print the solution

!       ifail: behaviour on error exit
!              =0 for hard exit, =1 for quiet-soft, =-1 for noisy-soft
ifail = 0
Call x04caf('General',' ',n,nrhs,b,ldb,'Solution(s)',ifail)

Else
Write (nout,99999) 'The (', info, ',', info, ')',                      &
' element of the factor U is zero'
End If

99999 Format (1X,A,I3,A,I3,A,A)
End Program f07cefe
```