Program f07cefe ! F07CEF Example Program Text ! Mark 24 Release. NAG Copyright 2012. ! .. 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 Read (nin,*) Read (nin,*) n, nrhs 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 (nin,*) du(1:n-1) Read (nin,*) d(1:n) Read (nin,*) dl(1:n-1) ! Read the right hand matrix B Read (nin,*)(b(i,1:nrhs),i=1,n) ! 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