PROGRAM f07jvfe ! F07JVF Example Program Text ! Mark 23 Release. NAG Copyright 2011. ! .. Use Statements .. USE nag_library, ONLY : nag_wp, x04dbf, zptrfs, zpttrf, zpttrs ! .. Implicit None Statement .. IMPLICIT NONE ! .. Parameters .. INTEGER, PARAMETER :: nin = 5, nout = 6 ! .. Local Scalars .. INTEGER :: i, ifail, info, ldb, ldx, n, nrhs ! .. Local Arrays .. COMPLEX (KIND=nag_wp), ALLOCATABLE :: b(:,:), e(:), ef(:), work(:), & x(:,:) REAL (KIND=nag_wp), ALLOCATABLE :: berr(:), d(:), df(:), ferr(:), & rwork(:) CHARACTER (1) :: clabs(1), rlabs(1) ! .. Executable Statements .. WRITE (nout,*) 'F07JVF 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),e(n-1),ef(n-1),work(n),x(ldx,nrhs),berr(nrhs), & d(n),df(n),ferr(nrhs),rwork(n)) ! 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 zptrrf is f07jrf CALL zpttrf(n,df,ef,info) IF (info==0) THEN ! Solve the equations AX = B ! The NAG name equivalent of zptrrs is f07jsf CALL zpttrs('Lower',n,nrhs,df,ef,x,ldx,info) ! Improve the solution and compute error estimates ! The NAG name equivalent of zptrfs is f07jvf CALL zptrfs('Lower',n,nrhs,d,e,df,ef,b,ldb,x,ldx,ferr,berr,work, & rwork,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 x04dbf('General',' ',n,nrhs,x,ldx,'Bracketed','F7.4', & 'Solution(s)','Integer',rlabs,'Integer',clabs,80,0,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 f07jvfe