Program dgtsv_example ! DGTSV Example Program Text ! Copyright 2017, Numerical Algorithms Group Ltd. http://www.nag.com ! .. Use Statements .. Use lapack_interfaces, Only: dgtsv Use lapack_precision, Only: dp ! .. Implicit None Statement .. Implicit None ! .. Parameters .. Integer, Parameter :: nin = 5, nout = 6 ! .. Local Scalars .. Integer :: info, n ! .. Local Arrays .. Real (Kind=dp), Allocatable :: b(:), d(:), dl(:), du(:) ! .. Executable Statements .. Write (nout, *) 'DGTSV 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 Call dgtsv(n, 1, dl, d, du, b, n, info) If (info==0) Then ! Print solution Write (nout, *) 'Solution' Write (nout, 100) b(1:n) Else Write (nout, 110) 'The (', info, ',', info, ')', & ' element of the factor U is zero' End If 100 Format ((1X,7F11.4)) 110 Format (1X, A, I3, A, I3, A, A) End Program