* F08GBF Example Program Text * Mark 21 Release. NAG Copyright 2004. * .. Parameters .. INTEGER NIN, NOUT PARAMETER (NIN=5,NOUT=6) INTEGER NMAX, MMAX PARAMETER (NMAX=10,MMAX=5) INTEGER LDZ PARAMETER (LDZ=NMAX) CHARACTER UPLO PARAMETER (UPLO='U') DOUBLE PRECISION ZERO PARAMETER (ZERO=0.0D+0) * .. Local Scalars .. DOUBLE PRECISION ABSTOL, VL, VU INTEGER I, IFAIL, IL, INFO, IU, J, M, N * .. Local Arrays .. DOUBLE PRECISION AP((NMAX*(NMAX+1))/2), W(NMAX), WORK(8*NMAX), + Z(LDZ,MMAX) INTEGER IWORK(5*NMAX), JFAIL(NMAX) * .. External Subroutines .. EXTERNAL DSPEVX, X04CAF * .. Executable Statements .. WRITE (NOUT,*) 'F08GBF 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 or lower triangular part of the matrix A * from data file * READ (NIN,*) VL, VU IF (UPLO.EQ.'U') THEN READ (NIN,*) ((AP(I+(J*(J-1))/2),J=I,N),I=1,N) ELSE IF (UPLO.EQ.'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 symmetric eigenvalue problem * CALL DSPEVX('Vectors','Values in range',UPLO,N,AP,VL,VU,IL,IU, + ABSTOL,M,W,Z,LDZ,WORK,IWORK,JFAIL,INFO) * IF (INFO.GE.0 .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) (JFAIL(J),J=1,M) END IF ELSE IF (M.GT.MMAX) THEN WRITE (NOUT,99996) 'M greater than MMAX, M =', M, + ', MMAX =', MMAX ELSE WRITE (NOUT,99999) 'Failure in DSPEVX. INFO =', INFO END IF ELSE WRITE (NOUT,*) WRITE (NOUT,*) 'NMAX too small' END IF * 99999 FORMAT (1X,A,I5) 99998 FORMAT (3X,(8F8.4)) 99997 FORMAT (3X,(8I8)) 99996 FORMAT (1X,A,I5,A,I5) END