Program f07jhfe ! F07JHF Example Program Text ! Mark 24 Release. NAG Copyright 2012. ! .. Use Statements .. Use nag_library, Only: dptrfs, dpttrf, dpttrs, nag_wp, x04caf ! .. Implicit None Statement .. Implicit None ! .. Parameters .. Integer, Parameter :: nin = 5, nout = 6 ! .. Local Scalars .. Integer :: i, ifail, info, ldb, ldx, n, nrhs ! .. Local Arrays .. Real (Kind=nag_wp), Allocatable :: b(:,:), berr(:), d(:), df(:), e(:), & ef(:), ferr(:), work(:), x(:,:) ! .. Executable Statements .. Write (nout,*) 'F07JHF Example Program Results' Write (nout,*) Flush (nout) ! Skip heading in data file Read (nin,*) Read (nin,*) n, nrhs ldb = n ldx = n Allocate (b(ldb,nrhs),berr(nrhs),d(n),df(n),e(n-1),ef(n-1),ferr(nrhs), & work(2*n),x(ldx,nrhs)) ! Read the lower bidiagonal part of the tridiagonal matrix A from ! data file Read (nin,*) d(1:n) Read (nin,*) e(1:n-1) ! Read the right hand matrix B Read (nin,*)(b(i,1:nrhs),i=1,n) ! Copy A into DF and EF, and copy B into X df(1:n) = d(1:n) ef(1:n-1) = e(1:n-1) x(1:n,1:nrhs) = b(1:n,1:nrhs) ! Factorize the copy of the tridiagonal matrix A ! The NAG name equivalent of dpttrf is f07jdf Call dpttrf(n,df,ef,info) If (info==0) Then ! Solve the equations AX = B ! The NAG name equivalent of dpttrs is f07jef Call dpttrs(n,nrhs,df,ef,x,ldx,info) ! Improve the solution and compute error estimates ! The NAG name equivalent of dptrfs is f07jhf Call dptrfs(n,nrhs,d,e,df,ef,b,ldb,x,ldx,ferr,berr,work,info) ! Print the solution and the forward and backward error ! estimates ! ifail: behaviour on error exit ! =0 for hard exit, =1 for quiet-soft, =-1 for noisy-soft ifail = 0 Call x04caf('General',' ',n,nrhs,x,ldx,'Solution(s)',ifail) Write (nout,*) Write (nout,*) 'Backward errors (machine-dependent)' Write (nout,99999) berr(1:nrhs) Write (nout,*) Write (nout,*) 'Estimated forward error bounds (machine-dependent)' Write (nout,99999) ferr(1:nrhs) Else Write (nout,99998) 'The leading minor of order ', info, & ' is not positive definite' End If 99999 Format ((3X,1P,7E11.1)) 99998 Format (1X,A,I3,A) End Program f07jhfe