PROGRAM f08hefe ! F08HEF Example Program Text ! Mark 23 Release. NAG Copyright 2011. ! .. Use Statements .. USE nag_library, ONLY : dsbtrd, dsteqr, nag_wp, x04caf ! .. Implicit None Statement .. IMPLICIT NONE ! .. Parameters .. INTEGER, PARAMETER :: nin = 5, nout = 6 ! .. Local Scalars .. INTEGER :: i, ifail, info, j, kd, ldab, ldq, n CHARACTER (1) :: uplo ! .. Local Arrays .. REAL (KIND=nag_wp), ALLOCATABLE :: ab(:,:), d(:), e(:), q(:,:), work(:) ! .. Intrinsic Functions .. INTRINSIC max, min ! .. Executable Statements .. WRITE (nout,*) 'F08HEF Example Program Results' ! Skip heading in data file READ (nin,*) READ (nin,*) n, kd ldab = kd + 1 ldq = n ALLOCATE (ab(ldab,n),d(n),e(n-1),q(ldq,n),work(2*n-2)) ! Read A from data file READ (nin,*) uplo IF (uplo=='U') THEN DO i = 1, n READ (nin,*) (ab(kd+1+i-j,j),j=i,min(n,i+kd)) END DO ELSE IF (uplo=='L') THEN DO i = 1, n READ (nin,*) (ab(1+i-j,j),j=max(1,i-kd),i) END DO END IF ! Reduce A to tridiagonal form T = (Q**T)*A*Q (and form Q) ! The NAG name equivalent of dsbtrd is f08hef CALL dsbtrd('V',uplo,n,kd,ab,ldab,d,e,q,ldq,work,info) ! Calculate all the eigenvalues and eigenvectors of A ! The NAG name equivalent of dsteqr is f08jef CALL dsteqr('V',n,d,e,q,ldq,work,info) WRITE (nout,*) IF (info>0) THEN WRITE (nout,*) 'Failure to converge.' ELSE ! Print eigenvalues and eigenvectors WRITE (nout,*) 'Eigenvalues' WRITE (nout,99999) d(1:n) WRITE (nout,*) FLUSH (nout) ! Normalize the eigenvectors DO i = 1, n q(1:n,i) = q(1:n,i)/q(1,i) END DO ! ifail: behaviour on error exit ! =0 for hard exit, =1 for quiet-soft, =-1 for noisy-soft ifail = 0 CALL x04caf('General',' ',n,n,q,ldq,'Eigenvectors',ifail) END IF 99999 FORMAT (3X,(8F8.4)) END PROGRAM f08hefe