PROGRAM f08fbfe ! F08FBF Example Program Text ! Mark 23 Release. NAG Copyright 2011. ! .. Use Statements .. USE nag_library, ONLY : dsyevx, nag_wp, x04caf ! .. Implicit None Statement .. IMPLICIT NONE ! .. Parameters .. REAL (KIND=nag_wp), PARAMETER :: zero = 0.0E+0_nag_wp INTEGER, PARAMETER :: nb = 64, nin = 5, nout = 6 ! .. Local Scalars .. REAL (KIND=nag_wp) :: abstol, vl, vu INTEGER :: i, ifail, il, info, iu, lda, ldz, & lwork, m, n ! .. Local Arrays .. REAL (KIND=nag_wp), ALLOCATABLE :: a(:,:), w(:), work(:), z(:,:) REAL (KIND=nag_wp) :: dummy(1) INTEGER, ALLOCATABLE :: iwork(:), jfail(:) ! .. Intrinsic Functions .. INTRINSIC max, nint ! .. Executable Statements .. WRITE (nout,*) 'F08FBF Example Program Results' WRITE (nout,*) ! Skip heading in data file READ (nin,*) READ (nin,*) n lda = n ldz = n m = n ALLOCATE (a(lda,n),w(n),z(ldz,m),iwork(5*n),jfail(n)) ! Read the lower and upper bounds of the interval to be searched. READ (nin,*) vl, vu ! Use routine workspace query to get optimal workspace. ! The NAG name equivalent of dsyevx is f08fbf lwork = -1 CALL dsyevx('Vectors','Values in range','Upper',n,a,lda,vl,vu,il,iu, & abstol,m,w,z,ldz,dummy,lwork,iwork,jfail,info) ! Make sure that there is enough workspace for blocksize nb. lwork = max((nb+3)*n,nint(dummy(1))) ALLOCATE (work(lwork)) ! Read the upper triangular part of the matrix A. READ (nin,*) (a(i,i:n),i=1,n) ! Set the absolute error tolerance for eigenvalues. With ABSTOL ! set to zero, the default value is used instead abstol = zero ! Solve the symmetric eigenvalue problem ! The NAG name equivalent of dsyevx is f08fbf CALL dsyevx('Vectors','Values in range','Upper',n,a,lda,vl,vu,il,iu, & abstol,m,w,z,ldz,work,lwork,iwork,jfail,info) IF (info>=0) THEN ! Print solution WRITE (nout,99999) 'Number of eigenvalues found =', m WRITE (nout,*) WRITE (nout,*) 'Eigenvalues' WRITE (nout,99998) w(1:m) FLUSH (nout) ! Normalize the eigenvectors DO i = 1, m 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,m,z,ldz,'Selected eigenvectors',ifail) IF (info>0) THEN WRITE (nout,99999) 'INFO eigenvectors failed to converge, INFO =' & , info WRITE (nout,*) 'Indices of eigenvectors that did not converge' WRITE (nout,99997) jfail(1:m) END IF ELSE WRITE (nout,99999) 'Failure in DSYEVX. INFO =', info END IF 99999 FORMAT (1X,A,I5) 99998 FORMAT (3X,(8F8.4)) 99997 FORMAT (3X,(8I8)) END PROGRAM f08fbfe