Program f07cafe
! F07CAF Example Program Text
! Mark 30.1 Release. NAG Copyright 2024.
! .. Use Statements ..
Use nag_library, Only: dgtsv, nag_wp
! .. Implicit None Statement ..
Implicit None
! .. Parameters ..
Integer, Parameter :: nin = 5, nout = 6
! .. Local Scalars ..
Integer :: info, n
! .. Local Arrays ..
Real (Kind=nag_wp), Allocatable :: b(:), d(:), dl(:), du(:)
! .. Executable Statements ..
Write (nout,*) 'F07CAF Example Program Results'
Write (nout,*)
! Skip heading in data file
Read (nin,*)
Read (nin,*) n
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
Read (nin,*) du(1:n-1)
Read (nin,*) d(1:n)
Read (nin,*) dl(1:n-1)
Read (nin,*) b(1:n)
! Solve the equations Ax = b for x
! The NAG name equivalent of dgtsv is f07caf
Call dgtsv(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 ((1X,7F11.4))
99998 Format (1X,A,I3,A,I3,A,A)
End Program f07cafe