## MB03FZ

### Eigenvalues and right deflating subspace of a complex skew-Hamiltonian/Hamiltonian pencil in factored form

[Specification] [Arguments] [Method] [References] [Comments] [Example]

Purpose

      To compute the eigenvalues of a complex N-by-N skew-Hamiltonian/
      Hamiltonian pencil aS - bH, with

                              (  B  F  )      (  Z11  Z12  )
        S = J Z' J' Z and H = (        ), Z = (            ),
                              (  G -B' )      (  Z21  Z22  )
                                                                    (1)
            (  0  I  )
        J = (        ).
            ( -I  0  )

      The structured Schur form of the embedded real skew-Hamiltonian/

      skew-Hamiltonian pencil, aB_S - bB_T, with B_S = J B_Z' J' B_Z,

              (  Re(Z11)  -Im(Z11)  |  Re(Z12)  -Im(Z12)  )
              (                     |                     )
              (  Im(Z11)   Re(Z11)  |  Im(Z12)   Re(Z12)  )
              (                     |                     )
        B_Z = (---------------------+---------------------) ,
              (                     |                     )
              (  Re(Z21)  -Im(Z21)  |  Re(Z22)  -Im(Z22)  )
              (                     |                     )
              (  Im(Z21)   Re(Z21)  |  Im(Z22)   Re(Z22)  )
                                                                     (2)
              ( -Im(B)  -Re(B)  | -Im(F)  -Re(F)  )
              (                 |                 )
              (  Re(B)  -Im(B)  |  Re(F)  -Im(F)  )
              (                 |                 )
        B_T = (-----------------+-----------------) ,  T = i*H,
              (                 |                 )
              ( -Im(G)  -Re(G)  | -Im(B')  Re(B') )
              (                 |                 )
              (  Re(G)  -Im(G)  | -Re(B') -Im(B') )

      is determined and used to compute the eigenvalues. Optionally, if
      COMPQ = 'C', an orthonormal basis of the right deflating subspace,
      Def_-(S, H), of the pencil aS - bH in (1), corresponding to the
      eigenvalues with strictly negative real part, is computed. Namely,
      after transforming aB_S - bB_H, in the factored form, by unitary
      matrices, we have B_Sout = J B_Zout' J' B_Zout,

                 ( BA  BD  )              ( BB  BF  )
        B_Zout = (         ) and B_Hout = (         ),               (3)
                 (  0  BC  )              (  0 -BB' )

      and the eigenvalues with strictly negative real part of the
      complex pencil aB_Sout - bB_Hout are moved to the top. The
      notation M' denotes the conjugate transpose of the matrix M.
      Optionally, if COMPU = 'C', an orthonormal basis of the companion
      subspace, range(P_U) [1], which corresponds to the eigenvalues
      with negative real part, is computed. The embedding doubles the
      multiplicities of the eigenvalues of the pencil aS - bH.

Specification

          SUBROUTINE MB03FZ( COMPQ, COMPU, ORTH, N, Z, LDZ, B, LDB, FG,
         $                   LDFG, NEIG, D, LDD, C, LDC, Q, LDQ, U, LDU,
         $                   ALPHAR, ALPHAI, BETA, IWORK, LIWORK, DWORK,
         $                   LDWORK, ZWORK, LZWORK, BWORK, INFO )
    C     .. Scalar Arguments ..
          CHARACTER          COMPQ, COMPU, ORTH
          INTEGER            INFO, LDB, LDC, LDD, LDFG, LDQ, LDU, LDWORK,
         $                   LDZ, LIWORK, LZWORK, N, NEIG
    C     .. Array Arguments ..
          LOGICAL            BWORK( * )
          INTEGER            IWORK( * )
          DOUBLE PRECISION   ALPHAI( * ), ALPHAR( * ), BETA( * ), DWORK( * )
          COMPLEX*16         B( LDB, * ), C( LDC, * ), D( LDD, * ),
         $                   FG( LDFG, * ), Q( LDQ, * ), U( LDU, * ),
         $                   Z( LDZ, * ), ZWORK( * )

Arguments

Mode Parameters

      COMPQ   CHARACTER*1
              Specifies whether to compute the right deflating subspace
              corresponding to the eigenvalues of aS - bH with strictly
              negative real part.
              = 'N': do not compute the deflating subspace;
              = 'C': compute the deflating subspace and store it in the
                     leading subarray of Q.

      COMPU   CHARACTER*1
              Specifies whether to compute the companion subspace
              corresponding to the eigenvalues of aS - bH with strictly
              negative real part.
              = 'N': do not compute the companion subspace;
              = 'C': compute the companion subspace and store it in the
                     leading subarray of U.

      ORTH    CHARACTER*1
              If COMPQ = 'C' or COMPU = 'C', specifies the technique for
              computing the orthonormal bases of the deflating subspace
              and companion subspace, as follows:
              = 'P':  QR factorization with column pivoting;
              = 'S':  singular value decomposition.
              If COMPQ = 'N' and COMPU = 'N', the ORTH value is not
              used.

Input/Output Parameters

      N       (input) INTEGER
              Order of the pencil aS - bH.  N >= 0, even.

      Z       (input/output) COMPLEX*16 array, dimension (LDZ, N)
              On entry, the leading N-by-N part of this array must
              contain the non-trivial factor Z in the factorization
              S = J Z' J' Z of the skew-Hamiltonian matrix S.
              On exit, if COMPQ = 'C' or COMPU = 'C', the leading
              N-by-N part of this array contains the upper triangular
              matrix BA in (3) (see also METHOD). The strictly lower
              triangular part is not zeroed.
              If COMPQ = 'N' and COMPU = 'N', this array is unchanged
              on exit.

      LDZ     INTEGER
              The leading dimension of the array Z.  LDZ >= MAX(1, N).

      B       (input/output) COMPLEX*16 array, dimension (LDB, N)
              On entry, the leading N/2-by-N/2 part of this array must
              contain the matrix B.
              On exit, if COMPQ = 'C' or COMPU = 'C', the leading
              N-by-N part of this array contains the upper triangular
              matrix BB in (3) (see also METHOD). The strictly lower
              triangular part is not zeroed.
              If COMPQ = 'N' and COMPU = 'N', this array is unchanged
              on exit.

      LDB     INTEGER
              The leading dimension of the array B.  LDB >= MAX(1, N).

      FG      (input/output) COMPLEX*16 array, dimension (LDFG, N)
              On entry, the leading N/2-by-N/2 lower triangular part of
              this array must contain the lower triangular part of the
              Hermitian matrix G, and the N/2-by-N/2 upper triangular
              part of the submatrix in the columns 2 to N/2+1 of this
              array must contain the upper triangular part of the
              Hermitian matrix F.
              On exit, if COMPQ = 'C' or COMPU = 'C', the leading
              N-by-N part of this array contains the Hermitian matrix
              BF in (3) (see also METHOD). The strictly lower triangular
              part of the input matrix is preserved. The diagonal
              elements might have tiny imaginary parts.
              If COMPQ = 'N' and COMPU = 'N', this array is unchanged
              on exit.

      LDFG    INTEGER
              The leading dimension of the array FG.  LDFG >= MAX(1, N).

      NEIG    (output) INTEGER
              If COMPQ = 'C' or COMPU = 'C', the number of eigenvalues
              in aS - bH with strictly negative real part.

      D       (output) COMPLEX*16 array, dimension (LDD, N)
              If COMPQ = 'C' or COMPU = 'C', the leading N-by-N part of
              this array contains the matrix BD in (3) (see METHOD).
              If COMPQ = 'N' and COMPU = 'N', this array is not
              referenced.

      LDD     INTEGER
              The leading dimension of the array D.
              LDD >= 1,         if COMPQ = 'N' and COMPU = 'N';
              LDD >= MAX(1, N), if COMPQ = 'C' or  COMPU = 'C'.

      C       (output) COMPLEX*16 array, dimension (LDC, N)
              If COMPQ = 'C' or COMPU = 'C', the leading N-by-N part of
              this array contains the lower triangular matrix BC in (3)
              (see also METHOD). The strictly upper triangular part is
              not zeroed.
              If COMPQ = 'N' and COMPU = 'N', this array is not
              referenced.

      LDC     INTEGER
              The leading dimension of the array C.
              LDC >= 1,         if COMPQ = 'N' and COMPU = 'N';
              LDC >= MAX(1, N), if COMPQ = 'C' or  COMPU = 'C'.

      Q       (output) COMPLEX*16 array, dimension (LDQ, 2*N)
              On exit, if COMPQ = 'C', the leading N-by-NEIG part of
              this array contains an orthonormal basis of the right
              deflating subspace corresponding to the eigenvalues of the
              pencil aS - bH with strictly negative real part.
              The remaining entries are meaningless.
              If COMPQ = 'N', this array is not referenced.

      LDQ     INTEGER
              The leading dimension of the array Q.
              LDQ >= 1,           if COMPQ = 'N';
              LDQ >= MAX(1, 2*N), if COMPQ = 'C'.

      U       (output) COMPLEX*16 array, dimension (LDU, 2*N)
              On exit, if COMPU = 'C', the leading N-by-NEIG part of
              this array contains an orthonormal basis of the companion
              subspace corresponding to the eigenvalues of the
              pencil aS - bH with strictly negative real part. The
              remaining entries are meaningless.
              If COMPU = 'N', this array is not referenced.

      LDU     INTEGER
              The leading dimension of the array U.
              LDU >= 1,         if COMPU = 'N';
              LDU >= MAX(1, N), if COMPU = 'C'.

      ALPHAR  (output) DOUBLE PRECISION array, dimension (N)
              The real parts of each scalar alpha defining an eigenvalue
              of the pencil aS - bH.

      ALPHAI  (output) DOUBLE PRECISION array, dimension (N)
              The imaginary parts of each scalar alpha defining an
              eigenvalue of the pencil aS - bH.
              If ALPHAI(j) is zero, then the j-th eigenvalue is real.

      BETA    (output) DOUBLE PRECISION array, dimension (N)
              The scalars beta that define the eigenvalues of the pencil
              aS - bH.
              Together, the quantities alpha = (ALPHAR(j),ALPHAI(j)) and
              beta = BETA(j) represent the j-th eigenvalue of the pencil
              aS - bH, in the form lambda = alpha/beta. Since lambda may
              overflow, the ratios should not, in general, be computed.

Workspace

      IWORK   INTEGER array, dimension (LIWORK)

      LIWORK  INTEGER
              The dimension of the array IWORK.  LIWORK >= 2*N+9.

      DWORK   DOUBLE PRECISION array, dimension (LDWORK)
              On exit, if INFO = 0, DWORK(1) returns the optimal LDWORK.
              On exit, if INFO = -26, DWORK(1) returns the minimum
              value of LDWORK.

      LDWORK  INTEGER
              The dimension of the array DWORK.
              LDWORK >= c*N**2 + N + MAX(6*N, 27), where
                        c = 18, if                 COMPU = 'C';
                        c = 16, if COMPQ = 'C' and COMPU = 'N';
                        c = 13, if COMPQ = 'N' and COMPU = 'N'.
              For good performance LDWORK should be generally larger.

              If LDWORK = -1, then a workspace query is assumed;
              the routine only calculates the optimal size of the
              DWORK array, returns this value as the first entry of
              the DWORK array, and no error message related to LDWORK
              is issued by XERBLA.

      ZWORK   COMPLEX*16 array, dimension (LZWORK)
              On exit, if INFO = 0, ZWORK(1) returns the optimal LZWORK.
              On exit, if INFO = -28, ZWORK(1) returns the minimum
              value of LZWORK.

      LZWORK  INTEGER
              The dimension of the array ZWORK.
              LZWORK >= 8*N + 28, if COMPQ = 'C';
              LZWORK >= 6*N + 28, if COMPQ = 'N' and COMPU = 'C';
              LZWORK >= 1,        if COMPQ = 'N' and COMPU = 'N'.
              For good performance LZWORK should be generally larger.

              If LZWORK = -1, then a workspace query is assumed;
              the routine only calculates the optimal size of the
              ZWORK array, returns this value as the first entry of
              the ZWORK array, and no error message related to LZWORK
              is issued by XERBLA.

      BWORK   LOGICAL array, dimension (LBWORK)
              LBWORK >= 0, if COMPQ = 'N' and COMPU = 'N';
              LBWORK >= N, if COMPQ = 'C' or  COMPU = 'C'.

Error Indicator

      INFO    INTEGER
              = 0: succesful exit;
              < 0: if INFO = -i, the i-th argument had an illegal value;
              = 1: the algorithm was not able to reveal information
                   about the eigenvalues from the 2-by-2 blocks in the
                   SLICOT Library routine MB03BD (called by MB04ED);
              = 2: periodic QZ iteration failed in the SLICOT Library
                   routines MB03BD or MB03BZ when trying to
                   triangularize the 2-by-2 blocks;
              = 3: the singular value decomposition failed in the LAPACK
                   routine ZGESVD (for ORTH = 'S').

Method

      First T = i*H is set. Then, the embeddings, B_Z and B_T, of the
      matrices S and T, are determined and, subsequently, the SLICOT
      Library routine MB04ED is applied to compute the structured Schur
      form, i.e., the factorizations

      ~                (  BZ11  BZ12  )
      B_Z = U' B_Z Q = (              ) and
                       (    0   BZ22  )

      ~                     (  T11  T12  )
      B_T = J Q' J' B_T Q = (            ),
                            (   0   T11' )

      where Q is real orthogonal, U is real orthogonal symplectic, BZ11,
      BZ22' are upper triangular and T11 is upper quasi-triangular.

      Second, the SLICOT Library routine MB03IZ is applied, to compute a
                     ~                                 ~
      unitary matrix Q and a unitary symplectic matrix U, such that

                    ~    ~
      ~  ~   ~   (  Z11  Z12  )
      U' B_Z Q = (       ~    ) =: B_Zout,
                 (   0   Z22  )

        ~        ~    ~   (  H11  H12  )
      J Q' J'(-i*B_T) Q = (            ) =: B_Hout,
                          (   0  -H11' )
           ~    ~
      with Z11, Z22', H11 upper triangular, and such that the spectrum

               ~       ~       ~
      Spec_-(J B_Z' J' B_Z, -i*B_T) is contained in the spectrum of the
                                                    ~    ~
      2*NEIG-by-2*NEIG leading principal subpencil aZ22'*Z11 - bH11.

      Finally, the right deflating subspace and the companion subspace
      are computed. See also page 21 in [1] for more details.

References

      [1] Benner, P., Byers, R., Mehrmann, V. and Xu, H.
          Numerical Computation of Deflating Subspaces of Embedded
          Hamiltonian Pencils.
          Tech. Rep. SFB393/99-15, Technical University Chemnitz,
          Germany, June 1999.

Numerical Aspects

                                                                3
      The algorithm is numerically backward stable and needs O(N )
      complex floating point operations.

Further Comments

      This routine does not perform any scaling of the matrices. Scaling
      might sometimes be useful, and it should be done externally.

Example

Program Text

    *     MB03FZ EXAMPLE PROGRAM TEXT
    *
    *     .. Parameters ..
          INTEGER            NIN, NOUT
          PARAMETER          ( NIN = 5, NOUT = 6 )
          INTEGER            NMAX
          PARAMETER          ( NMAX = 50 )
          INTEGER            LDB, LDC, LDD, LDFG, LDQ, LDU, LDWORK, LDZ,
         $                   LIWORK, LZWORK
          PARAMETER          ( LDB  = NMAX, LDC =   NMAX, LDD = NMAX,
         $                     LDFG = NMAX, LDQ = 2*NMAX, LDU = NMAX,
         $                     LDWORK = 18*NMAX*NMAX + NMAX + 3 +
         $                              MAX( 2*NMAX, 24 ), LDZ  = NMAX,
         $                     LIWORK = 2*NMAX + 9, LZWORK = 8*NMAX + 28 )
    *
    *     .. Local Scalars ..
          CHARACTER          COMPQ, COMPU, ORTH
          INTEGER            I, INFO, J, M, N, NEIG
    *
    *     .. Local Arrays ..
          COMPLEX*16         B( LDB, NMAX ), C( LDC, NMAX ), D( LDD, NMAX ),
         $                   FG( LDFG, NMAX ), Q( LDQ, 2*NMAX ),
         $                   U( LDU, 2*NMAX ), Z( LDZ, NMAX ),
         $                   ZWORK( LZWORK )
          DOUBLE PRECISION   ALPHAI( NMAX ),  ALPHAR( NMAX ), BETA( NMAX ),
         $                   DWORK( LDWORK )
          INTEGER            IWORK( LIWORK )
          LOGICAL            BWORK( NMAX )
    *
    *     .. External Functions ..
          LOGICAL            LSAME
          EXTERNAL           LSAME
    *
    *     .. External Subroutines ..
          EXTERNAL           MB03FZ
    *
    *     .. Intrinsic Functions ..
          INTRINSIC          MAX, MOD
    *
    *     .. Executable Statements ..
    *
          WRITE( NOUT, FMT = 99999 )
    *     Skip the heading in the data file and read in the data.
          READ( NIN, FMT = * )
          READ( NIN, FMT = * ) COMPQ, COMPU, ORTH, N
          IF( N.LT.0 .OR. N.GT.NMAX .OR. MOD( N, 2 ).NE.0 ) THEN
             WRITE( NOUT, FMT = 99998 ) N
          ELSE
             M = N/2
             READ( NIN, FMT = * ) ( (  Z( I, J ), J = 1, N   ), I = 1, N )
             READ( NIN, FMT = * ) ( (  B( I, J ), J = 1, M   ), I = 1, M )
             READ( NIN, FMT = * ) ( ( FG( I, J ), J = 1, M+1 ), I = 1, M )
    *        Compute the eigenvalues and orthogonal bases of the right
    *        deflating subspace and companion subspace of a complex
    *        skew-Hamiltonian/Hamiltonian pencil, corresponding to the
    *        eigenvalues with strictly negative real part.
             CALL MB03FZ( COMPQ, COMPU, ORTH, N, Z, LDZ, B, LDB, FG, LDFG,
         $                NEIG, D, LDD, C, LDC, Q, LDQ, U, LDU, ALPHAR,
         $                ALPHAI, BETA, IWORK, LIWORK, DWORK, LDWORK, ZWORK,
         $                LZWORK, BWORK, INFO )
    *
             IF( INFO.NE.0 ) THEN
                WRITE( NOUT, FMT = 99997 ) INFO
             ELSE
                WRITE( NOUT, FMT = 99996 )
                DO 10 I = 1, N
                   WRITE( NOUT, FMT = 99995 ) ( Z( I, J ), J = 1, N )
       10       CONTINUE
                IF( LSAME( COMPQ, 'C' ) .OR. LSAME( COMPU, 'C' ) ) THEN
                   WRITE( NOUT, FMT = 99994 )
                   DO 20 I = 1, N
                      WRITE( NOUT, FMT = 99995 ) ( D( I, J ), J = 1, N )
       20          CONTINUE
                   WRITE( NOUT, FMT = 99993 )
                   DO 30 I = 1, N
                      WRITE( NOUT, FMT = 99995 ) ( C( I, J ), J = 1, N )
       30          CONTINUE
                   WRITE( NOUT, FMT = 99992 )
                   DO 40 I = 1, N
                      WRITE( NOUT, FMT = 99995 ) ( B( I, J ), J = 1, N )
       40          CONTINUE
                   WRITE( NOUT, FMT = 99991 )
                   DO 50 I = 1, N
                      WRITE( NOUT, FMT = 99995 ) ( FG( I, J ), J = 1, N )
       50          CONTINUE
                END IF
                WRITE( NOUT, FMT = 99990 )
                WRITE( NOUT, FMT = 99989 ) ( ALPHAR( I ), I = 1, N )
                WRITE( NOUT, FMT = 99988 )
                WRITE( NOUT, FMT = 99989 ) ( ALPHAI( I ), I = 1, N )
                WRITE( NOUT, FMT = 99987 )
                WRITE( NOUT, FMT = 99989 ) (   BETA( I ), I = 1, N )
                IF( LSAME( COMPQ, 'C' ) .AND. NEIG.GT.0 ) THEN
                   WRITE( NOUT, FMT = 99986 )
                   DO 60 I = 1, N
                      WRITE( NOUT, FMT = 99995 ) ( Q( I, J ), J = 1, NEIG )
       60          CONTINUE
                END IF
                IF( LSAME( COMPU, 'C' ) .AND. NEIG.GT.0 ) THEN
                   WRITE( NOUT, FMT = 99985 )
                   DO 70 I = 1, N
                      WRITE( NOUT, FMT = 99995 ) ( U( I, J ), J = 1, NEIG )
       70          CONTINUE
                END IF
                IF( LSAME( COMPQ, 'C' ) .OR. LSAME( COMPU, 'C' ) )
         $         WRITE( NOUT, FMT = 99984 ) NEIG
             END IF
          END IF
          STOP
    *
    99999 FORMAT ( 'MB03FZ EXAMPLE PROGRAM RESULTS', 1X )
    99998 FORMAT ( 'N is out of range.', /, 'N = ', I5 )
    99997 FORMAT ( 'INFO on exit from MB03FZ = ', I2 )
    99996 FORMAT (/'The matrix Z on exit is ' )
    99995 FORMAT ( 20( 1X, F9.4, SP, F9.4, S, 'i ') )
    99994 FORMAT (/'The matrix D is ' )
    99993 FORMAT (/'The matrix C is ' )
    99992 FORMAT (/'The matrix B on exit is ' )
    99991 FORMAT (/'The matrix F on exit is ' )
    99990 FORMAT (/'The vector ALPHAR is ' )
    99989 FORMAT ( 50( 1X, F8.4 ) )
    99988 FORMAT (/'The vector ALPHAI is ' )
    99987 FORMAT (/'The vector BETA is ' )
    99986 FORMAT (/'The deflating subspace corresponding to the ',
         $         'eigenvalues with negative real part is ' )
    99985 FORMAT (/'The companion subspace corresponding to the ',
         $         'eigenvalues with negative real part is ' )
    99984 FORMAT (/'The number of eigenvalues in the initial pencil with ',
         $         'negative real part is ', I2 )
          END

Program Data

    MB03FZ EXAMPLE PROGRAM DATA
    	C	C	P	4
       (0.0328,0.9611)   (0.6428,0.2585)   (0.7033,0.4254)   (0.2552,0.7053)
       (0.0501,0.2510)   (0.2827,0.8865)   (0.4719,0.5387)   (0.0389,0.5676)
       (0.5551,0.4242)   (0.0643,0.2716)   (0.1165,0.7875)   (0.9144,0.3891)
       (0.0539,0.7931)   (0.0408,0.2654)   (0.9912,0.0989)   (0.0991,0.6585)
       (0.0547,0.8726)   (0.4008,0.8722)
       (0.7423,0.6166)   (0.2631,0.5872)
        0.8740            0.3697           (0.9178,0.6418)
       (0.7748,0.5358)    0.1652            0.2441

Program Results

    MB03FZ EXAMPLE PROGRAM RESULTS

    The matrix Z on exit is
        1.1347  -0.1694i     0.0920  -0.0894i     0.5253  +0.0280i    -0.0597  +0.1098i
        0.0000  +0.0000i    -0.9874  -0.6015i     0.2523  -0.0600i     0.3178  -0.0902i
        0.5551  +0.4242i     0.0643  +0.2716i     0.7553  -0.3356i     0.4772  -0.3177i
        0.0539  +0.7931i     0.0408  +0.2654i     0.9912  +0.0989i     0.9064  -0.1055i

    The matrix D is
       -0.7634  -0.2773i    -0.8466  -0.9586i    -0.0308  -0.0175i    -0.2754  -0.0715i
        1.2612  -0.2643i    -0.7291  -0.3165i     0.0282  -0.1748i     0.4091  +0.0233i
        0.3773  -0.1536i    -0.3937  -0.0480i    -0.1635  +0.1617i    -0.1775  +0.1277i
        0.7540  -0.0280i    -0.6860  -0.8306i    -0.2446  +0.0943i    -0.0722  +0.0517i

    The matrix C is
        0.5063  +0.1548i     0.0000  +0.0000i     0.0000  +0.0000i     0.0000  +0.0000i
       -0.0046  +0.1049i     0.3884  +0.3420i     0.0000  +0.0000i     0.0000  +0.0000i
       -1.1206  +0.1313i    -0.2270  -0.1753i     0.4300  -0.6107i     0.0000  +0.0000i
       -0.6127  -0.1939i    -0.5713  -0.7913i     0.3739  -0.2943i    -1.1501  -0.0850i

    The matrix B on exit is
        0.3322  +1.9093i    -0.1216  -0.1193i    -0.0030  +0.0330i     0.0405  +0.0592i
        0.0000  +0.0000i     0.1863  -1.8998i     0.2983  +0.2974i     0.6636  +0.5916i
        0.0000  +0.0000i     0.0000  +0.0000i     0.4459  -0.7452i    -0.0625  +0.2197i
        0.0000  +0.0000i     0.0000  +0.0000i     0.0000  +0.0000i     0.1418  +0.7392i

    The matrix F on exit is
        0.0258  +0.0000i    -0.0878  +0.1090i     0.3547  +0.5306i    -0.0138  -0.8770i
        0.7748  +0.5358i     0.0864  +0.0000i    -0.3788  -0.2829i    -0.3303  -0.0415i
        0.0000  +0.0000i     0.0000  +0.0000i    -0.0184  +0.0000i     0.1077  -0.0795i
        0.0000  +0.0000i     0.0000  +0.0000i     0.0000  +0.0000i    -0.0938  +0.0000i

    The vector ALPHAR is
       0.4295  -0.4295   0.0000   0.0000

    The vector ALPHAI is
       1.5363   1.5363  -1.4069  -0.7153

    The vector BETA is
       0.5000   0.5000   1.0000   1.0000

    The deflating subspace corresponding to the eigenvalues with negative real part is
       -0.2249  +0.4158i
       -0.1984  -0.3100i
        0.7286  -0.0427i
        0.3282  -0.0251i

    The companion subspace corresponding to the eigenvalues with negative real part is
       -0.1542  -0.0712i
       -0.4162  -0.3021i
       -0.0806  -0.6946i
       -0.4580  -0.0889i

    The number of eigenvalues in the initial pencil with negative real part is  1

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