* F08NHF Example Program Text * Mark 20 Revised. NAG Copyright 2001. * .. Parameters .. INTEGER NIN, NOUT PARAMETER (NIN=5,NOUT=6) INTEGER NMAX, LDA, LDH, LWORK, LDVL, LDVR PARAMETER (NMAX=8,LDA=NMAX,LDH=NMAX,LWORK=64*NMAX,LDVL=1, + LDVR=NMAX) * .. Local Scalars .. INTEGER I, IFAIL, IHI, ILO, INFO, J, M, N * .. Local Arrays .. DOUBLE PRECISION A(LDA,NMAX), H(LDH,NMAX), SCALE(NMAX), TAU(NMAX), + VL(LDVL,1), VR(LDVR,NMAX), WI(NMAX), WORK(LWORK), + WR(NMAX) LOGICAL SELECT(1) * .. External Subroutines .. EXTERNAL DGEBAK, DGEBAL, DGEHRD, DHSEQR, DORGHR, DTREVC, + F06QFF, X04CAF * .. Executable Statements .. WRITE (NOUT,*) 'F08NHF 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) * * Balance A * CALL DGEBAL('Both',N,A,LDA,ILO,IHI,SCALE,INFO) * * Reduce A to upper Hessenberg form H = (Q**T)*A*Q * CALL DGEHRD(N,ILO,IHI,A,LDA,TAU,WORK,LWORK,INFO) * * Copy A to H * CALL F06QFF('General',N,N,A,LDA,H,LDH) * * Copy A into VR * CALL F06QFF('General',N,N,A,LDA,VR,LDVR) * * Form Q explicitly, storing the result in VR * CALL DORGHR(N,1,N,VR,LDVR,TAU,WORK,LWORK,INFO) * * Calculate the eigenvalues and Schur factorization of A * CALL DHSEQR('Schur form','Vectors',N,ILO,IHI,H,LDH,WR,WI,VR, + LDVR,WORK,LWORK,INFO) * WRITE (NOUT,*) IF (INFO.GT.0) THEN WRITE (NOUT,*) 'Failure to converge.' ELSE WRITE (NOUT,*) 'Eigenvalues' WRITE (NOUT,99999) (' (',WR(I),',',WI(I),')',I=1,N) * * Calculate the eigenvectors of A, storing the result in VR * CALL DTREVC('Right','Backtransform',SELECT,N,H,LDH,VL,LDVL, + VR,LDVR,N,M,WORK,INFO) * CALL DGEBAK('Both','Right',N,ILO,IHI,SCALE,M,VR,LDVR,INFO) * * Print eigenvectors * WRITE (NOUT,*) IFAIL = 0 * CALL X04CAF('General',' ',N,M,VR,LDVR, + 'Contents of array VR',IFAIL) * END IF END IF * 99999 FORMAT (1X,A,F8.4,A,F8.4,A) END