PROGRAM f07ahfe ! F07AHF Example Program Text ! Mark 23 Release. NAG Copyright 2011. ! .. Use Statements .. USE nag_library, ONLY : dgerfs, dgetrf, dgetrs, nag_wp, x04caf ! .. Implicit None Statement .. IMPLICIT NONE ! .. Parameters .. INTEGER, PARAMETER :: nin = 5, nout = 6 CHARACTER (1), PARAMETER :: trans = 'N' ! .. Local Scalars .. INTEGER :: i, ifail, info, lda, ldaf, ldb, ldx, & n, nrhs ! .. Local Arrays .. REAL (KIND=nag_wp), ALLOCATABLE :: a(:,:), af(:,:), b(:,:), berr(:), & ferr(:), work(:), x(:,:) INTEGER, ALLOCATABLE :: ipiv(:), iwork(:) ! .. Executable Statements .. WRITE (nout,*) 'F07AHF Example Program Results' ! Skip heading in data file READ (nin,*) READ (nin,*) n, nrhs lda = n ldaf = n ldb = n ldx = n ALLOCATE (a(lda,n),af(ldaf,n),b(ldb,nrhs),berr(nrhs),ferr(nrhs), & work(3*n),x(ldx,n),ipiv(n),iwork(n)) ! Read A and B from data file, and copy A to AF and B to X READ (nin,*) (a(i,1:n),i=1,n) READ (nin,*) (b(i,1:nrhs),i=1,n) af(1:n,1:n) = a(1:n,1:n) x(1:n,1:nrhs) = b(1:n,1:nrhs) ! Factorize A in the array AF ! The NAG name equivalent of dgetrf is f07adf CALL dgetrf(n,n,af,ldaf,ipiv,info) WRITE (nout,*) FLUSH (nout) IF (info==0) THEN ! Compute solution in the array X ! The NAG name equivalent of dgetrs is f07aef CALL dgetrs(trans,n,nrhs,af,ldaf,ipiv,x,ldx,info) ! Improve solution, and compute backward errors and ! estimated bounds on the forward errors ! The NAG name equivalent of dgerfs is f07ahf CALL dgerfs(trans,n,nrhs,a,lda,af,ldaf,ipiv,b,ldb,x,ldx,ferr,berr, & work,iwork,info) ! Print 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,x,ldx,'Solution(s)',ifail) WRITE (nout,*) WRITE (nout,*) 'Backward errors (machine-dependent)' WRITE (nout,99999) berr(1:nrhs) WRITE (nout,*) 'Estimated forward error bounds (machine-dependent)' WRITE (nout,99999) ferr(1:nrhs) ELSE WRITE (nout,*) 'The factor U is singular' END IF 99999 FORMAT ((3X,1P,7E11.1)) END PROGRAM f07ahfe