Program f07cdfe ! F07CDF Example Program Text ! Mark 24 Release. NAG Copyright 2012. ! .. Use Statements .. Use nag_library, Only: dgttrf, 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 :: d(:), dl(:), du(:), du2(:) Integer, Allocatable :: ipiv(:) ! .. Executable Statements .. Write (nout,*) 'F07CDF Example Program Results' Write (nout,*) ! Skip heading in data file Read (nin,*) Read (nin,*) n Allocate (d(n),dl(n-1),du(n-1),du2(n-2),ipiv(n)) ! Read the tridiagonal matrix A from data file Read (nin,*) du(1:n-1) Read (nin,*) d(1:n) Read (nin,*) dl(1:n-1) ! Factorize the tridiagonal matrix A ! The NAG name equivalent of dgttrf is f06cdf Call dgttrf(n,dl,d,du,du2,ipiv,info) If (info>0) Then Write (nout,99999) 'The (', info, ',', info, ')', & ' element of the factor U is zero' End If ! Print details of the factorization Write (nout,*) 'Details of factorization' Write (nout,*) Write (nout,*) ' Second super-diagonal of U' Write (nout,99998) du2(1:n-2) Write (nout,*) Write (nout,*) ' First super-diagonal of U' Write (nout,99998) du(1:n-1) Write (nout,*) Write (nout,*) ' Main diagonal of U' Write (nout,99998) d(1:n) Write (nout,*) Write (nout,*) ' Multipliers' Write (nout,99998) dl(1:n-1) Write (nout,*) Write (nout,*) ' Vector of interchanges' Write (nout,99997) ipiv(1:n) 99999 Format (1X,A,I3,A,I3,A,A) 99998 Format (1X,8F9.4) 99997 Format (1X,5I9) End Program f07cdfe