PROGRAM f08gpfe ! F08GPF Example Program Text ! Mark 23 Release. NAG Copyright 2011. ! .. Use Statements .. USE nag_library, ONLY : nag_wp, x04daf, zhpevx ! .. 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, ldz, m, n ! .. Local Arrays .. COMPLEX (KIND=nag_wp), ALLOCATABLE :: ap(:), work(:), z(:,:) REAL (KIND=nag_wp), ALLOCATABLE :: rwork(:), w(:) INTEGER, ALLOCATABLE :: iwork(:), jfail(:) ! .. Executable Statements .. WRITE (nout,*) 'F08GPF Example Program Results' WRITE (nout,*) ! Skip heading in data file READ (nin,*) READ (nin,*) n ldz = n m = n ALLOCATE (ap((n*(n+1))/2),work(2*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,*) ((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 ! Set the absolute error tolerance for eigenvalues. With ABSTOL ! set to zero, the default value is used instead abstol = zero ! Solve the Hermitian eigenvalue problem ! The NAG name equivalent of zhpevx is f08gpf CALL zhpevx('Vectors','Values in range',uplo,n,ap,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) ! 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 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 ZHPEVX. INFO =', info END IF 99999 FORMAT (1X,A,I5) 99998 FORMAT (3X,(8F8.4)) 99997 FORMAT (3X,(8I8)) END PROGRAM f08gpfe