* F08GFF Example Program Text * Mark 16 Release. NAG Copyright 1992. * .. Parameters .. INTEGER NIN, NOUT PARAMETER (NIN=5,NOUT=6) INTEGER NMAX, LDQ PARAMETER (NMAX=8,LDQ=NMAX) * .. Local Scalars .. INTEGER I, IFAIL, INFO, J, N CHARACTER UPLO * .. Local Arrays .. DOUBLE PRECISION AP(NMAX*(NMAX+1)/2), D(NMAX), E(NMAX), + Q(LDQ,NMAX), TAU(NMAX), WORK(2*NMAX-2) * .. External Subroutines .. EXTERNAL DOPGTR, DSPTRD, DSTEQR, X04CAF * .. Executable Statements .. WRITE (NOUT,*) 'F08GFF 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**T)*A*Q * CALL DSPTRD(UPLO,N,AP,D,E,TAU,INFO) * * Form Q explicitly, storing the result in Q * CALL DOPGTR(UPLO,N,AP,TAU,Q,LDQ,WORK,INFO) * * Calculate all the eigenvalues and eigenvectors of A * CALL DSTEQR('V',N,D,E,Q,LDQ,WORK,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 X04CAF('General',' ',N,N,Q,LDQ,'Eigenvectors',IFAIL) * END IF END IF * 99999 FORMAT (3X,(8F8.4)) END