* F08GTF Example Program Text * Mark 16 Release. NAG Copyright 1992. * .. Parameters .. INTEGER NIN, NOUT PARAMETER (NIN=5,NOUT=6) INTEGER NMAX, LDZ PARAMETER (NMAX=8,LDZ=NMAX) * .. Local Scalars .. INTEGER I, IFAIL, INFO, J, N CHARACTER UPLO * .. Local Arrays .. COMPLEX*16 AP(NMAX*(NMAX+1)/2), TAU(NMAX), WORK(NMAX-1), + Z(LDZ,NMAX) DOUBLE PRECISION D(NMAX), E(NMAX), RWORK(2*NMAX-2) CHARACTER CLABS(1), RLABS(1) * .. External Subroutines .. EXTERNAL X04DBF, ZHPTRD, ZSTEQR, ZUPGTR * .. Executable Statements .. WRITE (NOUT,*) 'F08GTF Example Program Results' * Skip heading in data file READ (NIN,*) READ (NIN,*) N IF (N.LE.NMAX) THEN * * Read A from data file * READ (NIN,*) UPLO 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 * * Reduce A to tridiagonal form T = (Q**H)*A*Q * CALL ZHPTRD(UPLO,N,AP,D,E,TAU,INFO) * * Form Q explicitly, storing the result in Z * CALL ZUPGTR(UPLO,N,AP,TAU,Z,LDZ,WORK,INFO) * * Calculate all the eigenvalues and eigenvectors of A * CALL ZSTEQR('V',N,D,E,Z,LDZ,RWORK,INFO) * WRITE (NOUT,*) IF (INFO.GT.0) THEN WRITE (NOUT,*) 'Failure to converge.' ELSE * * Print eigenvalues and eigenvectors * WRITE (NOUT,*) 'Eigenvalues' WRITE (NOUT,99999) (D(I),I=1,N) WRITE (NOUT,*) IFAIL = 0 * CALL X04DBF('General',' ',N,N,Z,LDZ,'Bracketed','F7.4', + 'Eigenvectors','Integer',RLABS,'Integer',CLABS, + 80,0,IFAIL) * END IF END IF STOP * 99999 FORMAT (8X,4(F7.4,11X,:)) END