PROGRAM f08jhfe ! F08JHF Example Program Text ! Mark 23 Release. NAG Copyright 2011. ! .. Use Statements .. USE nag_library, ONLY : dsbtrd, dstedc, nag_wp, x04caf ! .. Implicit None Statement .. IMPLICIT NONE ! .. Parameters .. INTEGER, PARAMETER :: nin = 5, nout = 6 CHARACTER (1), PARAMETER :: uplo = 'U' ! .. Local Scalars .. INTEGER :: i, ifail, info, j, kd, ldab, ldz, & lgn, liwork, lwork, n ! .. Local Arrays .. REAL (KIND=nag_wp), ALLOCATABLE :: ab(:,:), d(:), e(:), work(:), z(:,:) REAL (KIND=nag_wp) :: rdum(1) INTEGER :: idum(1) INTEGER, ALLOCATABLE :: iwork(:) ! .. Intrinsic Functions .. INTRINSIC ceiling, log, max, min, nint, real ! .. Executable Statements .. WRITE (nout,*) 'F08JHF Example Program Results' WRITE (nout,*) ! Skip heading in data file READ (nin,*) READ (nin,*) n, kd ldab = kd + 1 ldz = n lgn = ceiling(log(real(n,kind=nag_wp))/log(2.0E0_nag_wp)) ALLOCATE (ab(ldab,n),d(n),e(n-1),z(ldz,n)) ! Use routine workspace query to get optimal workspace. lwork = -1 liwork = -1 ! The NAG name equivalent of dstedc is f08jhf CALL dstedc('V',n,d,e,z,ldz,rdum,lwork,idum,liwork,info) ! Make sure that there is enough workspace. lwork = max(1+3*n+2*n*lgn+4*n*n,nint(rdum(1))) liwork = max(6+6*n+5*n*lgn,idum(1)) ALLOCATE (work(lwork),iwork(liwork)) ! Read the upper or lower triangular part of the band matrix A ! from data file 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 = (Z**T)*A*Z, and form Z ! The NAG name equivalent of dsbtrd is f08hef CALL dsbtrd('V',uplo,n,kd,ab,ldab,d,e,z,ldz,work,info) ! Calculate all the eigenvalues and eigenvectors of A, ! from T and Z ! The NAG name equivalent of dstedc is f08jhf CALL dstedc('V',n,d,e,z,ldz,work,lwork,iwork,liwork,info) IF (info==0) THEN ! Print eigenvalues and eigenvectors WRITE (nout,*) 'Eigenvalues' WRITE (nout,99999) d(1:n) WRITE (nout,*) FLUSH (nout) ! Normalize the eigenvectors DO i = 1, n z(1:n,i) = z(1:n,i)/z(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,z,ldz,'Eigenvectors',ifail) ELSE WRITE (nout,99998) 'Failure in DSTEDC. INFO = ', info END IF 99999 FORMAT ((3X,8F8.4)) 99998 FORMAT (1X,A,I10) END PROGRAM f08jhfe