PROGRAM f04befe ! F04BEF Example Program Text ! Mark 23 Release. NAG Copyright 2011. ! .. Use Statements .. USE nag_library, ONLY : f04bef, nag_wp, x04caf ! .. Implicit None Statement .. IMPLICIT NONE ! .. Parameters .. INTEGER, PARAMETER :: nin = 5, nout = 6 CHARACTER (1), PARAMETER :: uplo = 'U' ! .. Local Scalars .. REAL (KIND=nag_wp) :: errbnd, rcond INTEGER :: i, ierr, ifail, j, ldb, n, nrhs ! .. Local Arrays .. REAL (KIND=nag_wp), ALLOCATABLE :: ap(:), b(:,:) ! .. Executable Statements .. WRITE (nout,*) 'F04BEF Example Program Results' WRITE (nout,*) FLUSH (nout) ! Skip heading in data file READ (nin,*) READ (nin,*) n, nrhs ldb = n ALLOCATE (ap((n*(n+1))/2),b(ldb,nrhs)) ! Read the upper or lower triangular part of the matrix A from ! data file IF (uplo=='U') THEN READ (nin,*) ((ap(i+(j*(j-1))/2),j=i,n),i=1,n) ELSE IF (uplo=='L') THEN READ (nin,*) ((ap(i+((2*n-j)*(j-1))/2),j=1,i),i=1,n) END IF ! Read B from data file READ (nin,*) (b(i,1:nrhs),i=1,n) ! Solve the equations AX = B for X ! ifail: behaviour on error exit ! =0 for hard exit, =1 for quiet-soft, =-1 for noisy-soft ifail = 1 CALL f04bef(uplo,n,nrhs,ap,b,ldb,rcond,errbnd,ifail) IF (ifail==0) THEN ! Print solution, estimate of condition number and approximate ! error bound ierr = 0 CALL x04caf('General',' ',n,nrhs,b,ldb,'Solution',ierr) WRITE (nout,*) WRITE (nout,*) 'Estimate of condition number' WRITE (nout,99999) 1.0E0_nag_wp/rcond WRITE (nout,*) WRITE (nout,*) 'Estimate of error bound for computed solutions' WRITE (nout,99999) errbnd ELSE IF (ifail==n+1) THEN ! Matrix A is numerically singular. Print estimate of ! reciprocal of condition number and solution WRITE (nout,*) WRITE (nout,*) 'Estimate of reciprocal of condition number' WRITE (nout,99999) rcond WRITE (nout,*) FLUSH (nout) ierr = 0 CALL x04caf('General',' ',n,nrhs,b,ldb,'Solution',ierr) ELSE IF (ifail>0 .AND. ifail<=n) THEN ! The matrix A is not positive definite to working precision WRITE (nout,99998) 'The leading minor of order ', ifail, & ' is not positive definite' ELSE WRITE (nout,99997) ifail END IF 99999 FORMAT (6X,1P,E9.1) 99998 FORMAT (1X,A,I3,A) 99997 FORMAT (1X,' ** F04BEF returned with IFAIL = ',I5) END PROGRAM f04befe