* F08NFF Example Program Text * Mark 16 Release. NAG Copyright 1992. * .. Parameters .. INTEGER NIN, NOUT PARAMETER (NIN=5,NOUT=6) INTEGER NMAX, LDA, LDZ, LWORK PARAMETER (NMAX=8,LDA=NMAX,LDZ=NMAX,LWORK=64*(NMAX-1)) * .. Local Scalars .. INTEGER I, IFAIL, INFO, J, N * .. Local Arrays .. DOUBLE PRECISION A(LDA,NMAX), TAU(NMAX), WI(NMAX), WORK(LWORK), + WR(NMAX), Z(LDZ,NMAX) * .. External Subroutines .. EXTERNAL DGEHRD, DHSEQR, DORGHR, F06QFF, X04CAF * .. Executable Statements .. WRITE (NOUT,*) 'F08NFF 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,*) ((A(I,J),J=1,N),I=1,N) * * Reduce A to upper Hessenberg form H = (Q**T)*A*Q * CALL DGEHRD(N,1,N,A,LDA,TAU,WORK,LWORK,INFO) * * Copy A into Z * CALL F06QFF('General',N,N,A,LDA,Z,LDZ) * * Form Q explicitly, storing the result in Z * CALL DORGHR(N,1,N,Z,LDZ,TAU,WORK,LWORK,INFO) * * Calculate the Schur factorization of H = Y*T*(Y**T) and form * Q*Y explicitly, storing the result in Z * * Note that A = Z*T*(Z**T), where Z = Q*Y * CALL DHSEQR('Schur form','Vectors',N,1,N,A,LDA,WR,WI,Z,LDZ, + WORK,LWORK,INFO) * * Print Schur form * WRITE (NOUT,*) IFAIL = 0 * CALL X04CAF('General',' ',N,N,A,LDA,'Schur form',IFAIL) * * Print Schur vectors * WRITE (NOUT,*) IFAIL = 0 * CALL X04CAF('General',' ',N,N,Z,LDZ,'Schur vectors of A',IFAIL) * END IF * END