PROGRAM f08hpfe ! F08HPF Example Program Text ! Mark 23 Release. NAG Copyright 2011. ! .. Use Statements .. USE nag_library, ONLY : nag_wp, x04daf, zhbevx ! .. Implicit None Statement .. IMPLICIT NONE ! .. Parameters .. REAL (KIND=nag_wp), PARAMETER :: zero = 0.0E+0_nag_wp INTEGER, PARAMETER :: nin = 5, nout = 6 CHARACTER (1), PARAMETER :: uplo = 'U' ! .. Local Scalars .. REAL (KIND=nag_wp) :: abstol, vl, vu INTEGER :: i, ifail, il, info, iu, j, kd, ldab, & ldq, ldz, m, n ! .. Local Arrays .. COMPLEX (KIND=nag_wp), ALLOCATABLE :: ab(:,:), q(:,:), work(:), z(:,:) REAL (KIND=nag_wp), ALLOCATABLE :: rwork(:), w(:) INTEGER, ALLOCATABLE :: iwork(:), jfail(:) ! .. Intrinsic Functions .. INTRINSIC max, min ! .. Executable Statements .. WRITE (nout,*) 'F08HPF Example Program Results' WRITE (nout,*) ! Skip heading in data file READ (nin,*) READ (nin,*) n, kd ldab = kd + 1 ldq = n ldz = n m = n ALLOCATE (ab(ldab,n),q(ldq,n),work(n),z(ldz,m),rwork(7*n),w(n), & iwork(5*n),jfail(n)) ! Read the lower and upper bounds of the interval to be searched, ! and read the upper or lower triangular part of the matrix A ! from data file READ (nin,*) vl, vu IF (uplo=='U') THEN READ (nin,*) ((ab(kd+1+i-j,j),j=i,min(n,i+kd)),i=1,n) ELSE IF (uplo=='L') THEN READ (nin,*) ((ab(1+i-j,j),j=max(1,i-kd),i),i=1,n) END IF ! Set the absolute error tolerance for eigenvalues. With ABSTOL ! set to zero, the default value is used instead abstol = zero ! Solve the band symmetric eigenvalue problem ! The NAG name equivalent of zhbevx is f08hpf CALL zhbevx('Vectors','Values in range',uplo,n,kd,ab,ldab,q,ldq,vl,vu, & il,iu,abstol,m,w,z,ldz,work,rwork,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) ! ifail: behaviour on error exit ! =0 for hard exit, =1 for quiet-soft, =-1 for noisy-soft ifail = 0 CALL x04daf('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 ZHBEVX. INFO =', info END IF 99999 FORMAT (1X,A,I5) 99998 FORMAT (3X,(8F8.4)) 99997 FORMAT (3X,(8I8)) END PROGRAM f08hpfe