* F08SBF Example Program Text * Mark 21. NAG Copyright 2004. * .. Parameters .. INTEGER NIN, NOUT PARAMETER (NIN=5,NOUT=6) INTEGER NB, NMAX, MMAX PARAMETER (NB=64,NMAX=10,MMAX=5) INTEGER LDA, LDB, LDZ, LWORK PARAMETER (LDA=NMAX,LDB=NMAX,LDZ=NMAX,LWORK=(NB+3)*NMAX) DOUBLE PRECISION ZERO PARAMETER (ZERO=0.0D+0) * .. Local Scalars .. DOUBLE PRECISION ABSTOL, VL, VU INTEGER I, IFAIL, IL, INFO, IU, J, LWKOPT, M, N * .. Local Arrays .. DOUBLE PRECISION A(LDA,NMAX), B(LDB,NMAX), W(NMAX), WORK(LWORK), + Z(LDZ,MMAX) INTEGER INDEX(NMAX), IWORK(5*NMAX) * .. External Subroutines .. EXTERNAL DSYGVX, X04CAF * .. Executable Statements .. WRITE (NOUT,*) 'F08SBF Example Program Results' WRITE (NOUT,*) * Skip heading in data file READ (NIN,*) READ (NIN,*) N IF (N.LE.NMAX) THEN * * Read the lower and upper bounds of the interval to be searched, * and read the upper triangular parts of the matrices A and B * READ (NIN,*) VL, VU READ (NIN,*) ((A(I,J),J=I,N),I=1,N) READ (NIN,*) ((B(I,J),J=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 generalized symmetric eigenvalue problem * A*x = lambda*B*x (ITYPE = 1) * CALL DSYGVX(1,'Vectors','Values in range','Upper',N,A,LDA,B, + LDB,VL,VU,IL,IU,ABSTOL,M,W,Z,LDZ,WORK,LWORK,IWORK, + INDEX,INFO) LWKOPT = WORK(1) * IF (INFO.GE.0 .AND. INFO.LE.N .AND. M.LE.MMAX) THEN * * Print solution * WRITE (NOUT,99999) 'Number of eigenvalues found =', M WRITE (NOUT,*) WRITE (NOUT,*) 'Eigenvalues' WRITE (NOUT,99998) (W(J),J=1,M) * IFAIL = 0 CALL X04CAF('General',' ',N,M,Z,LDZ,'Selected eigenvectors', + IFAIL) IF (INFO.GT.0) THEN WRITE (NOUT,99999) + 'INFO eigenvectors failed to converge, INFO =', INFO WRITE (NOUT,*) + 'Indices of eigenvectors that did not converge' WRITE (NOUT,99997) (INDEX(J),J=1,M) END IF ELSE IF (INFO.GT.N .AND. INFO.LE.2*N) THEN I = INFO - N WRITE (NOUT,99996) 'The leading minor of order ', I, + ' of B is not positive definite' ELSE IF (M.GT.MMAX) THEN WRITE (NOUT,99995) 'M greater than MMAX, M =', M, + ', MMAX =', MMAX ELSE WRITE (NOUT,99999) 'Failure in DSYGVX. INFO =', INFO END IF * * Print workspace information * IF (LWORK.LT.LWKOPT) THEN WRITE (NOUT,*) WRITE (NOUT,99994) 'Optimum workspace required = ', LWKOPT, + 'Workspace provided = ', LWORK END IF ELSE WRITE (NOUT,*) WRITE (NOUT,*) 'NMAX too small' END IF STOP * 99999 FORMAT (1X,A,I5) 99998 FORMAT (3X,(8F8.4)) 99997 FORMAT (3X,(8I8)) 99996 FORMAT (1X,A,I4,A) 99995 FORMAT (1X,A,I5,A,I5) 99994 FORMAT (1X,A,I5,/1X,A,I5) END