SUBROUTINE ZUNBDB( TRANS, SIGNS, M, P, Q, X11, LDX11, X12, LDX12,
     $                   X21, LDX21, X22, LDX22, THETA, PHI, TAUP1,
     $                   TAUP2, TAUQ1, TAUQ2, WORK, LWORK, INFO )
      IMPLICIT NONE
*
*  -- LAPACK routine ((version 3.3.0)) --
*
*  -- Contributed by Brian Sutton of the Randolph-Macon College --
*  -- November 2010
*
*  -- LAPACK is a software package provided by Univ. of Tennessee,    --
*  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--     
*
*     .. Scalar Arguments ..
      CHARACTER          SIGNS, TRANS
      INTEGER            INFO, LDX11, LDX12, LDX21, LDX22, LWORK, M, P,
     $                   Q
*     ..
*     .. Array Arguments ..
      DOUBLE PRECISION   PHI( * ), THETA( * )
      COMPLEX*16         TAUP1( * ), TAUP2( * ), TAUQ1( * ), TAUQ2( * ),
     $                   WORK( * ), X11( LDX11, * ), X12( LDX12, * ),
     $                   X21( LDX21, * ), X22( LDX22, * )
*     ..
*
*  Purpose
*  =======
*
*  ZUNBDB simultaneously bidiagonalizes the blocks of an M-by-M
*  partitioned unitary matrix X:
*
*                                  [ B11 | B12 0  0 ]
*      [ X11 | X12 ]   [ P1 |    ] [  0  |  0 -I  0 ] [ Q1 |    ]**H
*  X = [-----------] = [---------] [----------------] [---------]   .
*      [ X21 | X22 ]   [    | P2 ] [ B21 | B22 0  0 ] [    | Q2 ]
*                                  [  0  |  0  0  I ]
*
*  X11 is P-by-Q. Q must be no larger than P, M-P, or M-Q. (If this is
*  not the case, then X must be transposed and/or permuted. This can be
*  done in constant time using the TRANS and SIGNS options. See ZUNCSD
*  for details.)
*
*  The unitary matrices P1, P2, Q1, and Q2 are P-by-P, (M-P)-by-
*  (M-P), Q-by-Q, and (M-Q)-by-(M-Q), respectively. They are
*  represented implicitly by Householder vectors.
*
*  B11, B12, B21, and B22 are Q-by-Q bidiagonal matrices represented
*  implicitly by angles THETA, PHI.
*
*  Arguments
*  =========
*
*  TRANS   (input) CHARACTER
*          = 'T':      X, U1, U2, V1T, and V2T are stored in row-major
*                      order;
*          otherwise:  X, U1, U2, V1T, and V2T are stored in column-
*                      major order.
*
*  SIGNS   (input) CHARACTER
*          = 'O':      The lower-left block is made nonpositive (the
*                      "other" convention);
*          otherwise:  The upper-right block is made nonpositive (the
*                      "default" convention).
*
*  M       (input) INTEGER
*          The number of rows and columns in X.
*
*  P       (input) INTEGER
*          The number of rows in X11 and X12. 0 <= P <= M.
*
*  Q       (input) INTEGER
*          The number of columns in X11 and X21. 0 <= Q <=
*          MIN(P,M-P,M-Q).
*
*  X11     (input/output) COMPLEX*16 array, dimension (LDX11,Q)
*          On entry, the top-left block of the unitary matrix to be
*          reduced. On exit, the form depends on TRANS:
*          If TRANS = 'N', then
*             the columns of tril(X11) specify reflectors for P1,
*             the rows of triu(X11,1) specify reflectors for Q1;
*          else TRANS = 'T', and
*             the rows of triu(X11) specify reflectors for P1,
*             the columns of tril(X11,-1) specify reflectors for Q1.
*
*  LDX11   (input) INTEGER
*          The leading dimension of X11. If TRANS = 'N', then LDX11 >=
*          P; else LDX11 >= Q.
*
*  X12     (input/output) COMPLEX*16 array, dimension (LDX12,M-Q)
*          On entry, the top-right block of the unitary matrix to
*          be reduced. On exit, the form depends on TRANS:
*          If TRANS = 'N', then
*             the rows of triu(X12) specify the first P reflectors for
*             Q2;
*          else TRANS = 'T', and
*             the columns of tril(X12) specify the first P reflectors
*             for Q2.
*
*  LDX12   (input) INTEGER
*          The leading dimension of X12. If TRANS = 'N', then LDX12 >=
*          P; else LDX11 >= M-Q.
*
*  X21     (input/output) COMPLEX*16 array, dimension (LDX21,Q)
*          On entry, the bottom-left block of the unitary matrix to
*          be reduced. On exit, the form depends on TRANS:
*          If TRANS = 'N', then
*             the columns of tril(X21) specify reflectors for P2;
*          else TRANS = 'T', and
*             the rows of triu(X21) specify reflectors for P2.
*
*  LDX21   (input) INTEGER
*          The leading dimension of X21. If TRANS = 'N', then LDX21 >=
*          M-P; else LDX21 >= Q.
*
*  X22     (input/output) COMPLEX*16 array, dimension (LDX22,M-Q)
*          On entry, the bottom-right block of the unitary matrix to
*          be reduced. On exit, the form depends on TRANS:
*          If TRANS = 'N', then
*             the rows of triu(X22(Q+1:M-P,P+1:M-Q)) specify the last
*             M-P-Q reflectors for Q2,
*          else TRANS = 'T', and
*             the columns of tril(X22(P+1:M-Q,Q+1:M-P)) specify the last
*             M-P-Q reflectors for P2.
*
*  LDX22   (input) INTEGER
*          The leading dimension of X22. If TRANS = 'N', then LDX22 >=
*          M-P; else LDX22 >= M-Q.
*
*  THETA   (output) DOUBLE PRECISION array, dimension (Q)
*          The entries of the bidiagonal blocks B11, B12, B21, B22 can
*          be computed from the angles THETA and PHI. See Further
*          Details.
*
*  PHI     (output) DOUBLE PRECISION array, dimension (Q-1)
*          The entries of the bidiagonal blocks B11, B12, B21, B22 can
*          be computed from the angles THETA and PHI. See Further
*          Details.
*
*  TAUP1   (output) COMPLEX*16 array, dimension (P)
*          The scalar factors of the elementary reflectors that define
*          P1.
*
*  TAUP2   (output) COMPLEX*16 array, dimension (M-P)
*          The scalar factors of the elementary reflectors that define
*          P2.
*
*  TAUQ1   (output) COMPLEX*16 array, dimension (Q)
*          The scalar factors of the elementary reflectors that define
*          Q1.
*
*  TAUQ2   (output) COMPLEX*16 array, dimension (M-Q)
*          The scalar factors of the elementary reflectors that define
*          Q2.
*
*  WORK    (workspace) COMPLEX*16 array, dimension (LWORK)
*
*  LWORK   (input) INTEGER
*          The dimension of the array WORK. LWORK >= M-Q.
*
*          If LWORK = -1, then a workspace query is assumed; the routine
*          only calculates the optimal size of the WORK array, returns
*          this value as the first entry of the WORK array, and no error
*          message related to LWORK is issued by XERBLA.
*
*  INFO    (output) INTEGER
*          = 0:  successful exit.
*          < 0:  if INFO = -i, the i-th argument had an illegal value.
*
*  Further Details
*  ===============
*
*  The bidiagonal blocks B11, B12, B21, and B22 are represented
*  implicitly by angles THETA(1), ..., THETA(Q) and PHI(1), ...,
*  PHI(Q-1). B11 and B21 are upper bidiagonal, while B21 and B22 are
*  lower bidiagonal. Every entry in each bidiagonal band is a product
*  of a sine or cosine of a THETA with a sine or cosine of a PHI. See
*  [1] or ZUNCSD for details.
*
*  P1, P2, Q1, and Q2 are represented as products of elementary
*  reflectors. See ZUNCSD for details on generating P1, P2, Q1, and Q2
*  using ZUNGQR and ZUNGLQ.
*
*  Reference
*  =========
*
*  [1] Brian D. Sutton. Computing the complete CS decomposition. Numer.
*      Algorithms, 50(1):33-65, 2009.
*
*  ====================================================================
*
*     .. Parameters ..
      DOUBLE PRECISION   REALONE
      PARAMETER          ( REALONE = 1.0D0 )
      COMPLEX*16         NEGONE, ONE
      PARAMETER          ( NEGONE = (-1.0D0,0.0D0),
     $                     ONE = (1.0D0,0.0D0) )
*     ..
*     .. Local Scalars ..
      LOGICAL            COLMAJOR, LQUERY
      INTEGER            I, LWORKMIN, LWORKOPT
      DOUBLE PRECISION   Z1, Z2, Z3, Z4
*     ..
*     .. External Subroutines ..
      EXTERNAL           ZAXPY, ZLARF, ZLARFGP, ZSCAL, XERBLA
      EXTERNAL           ZLACGV
*
*     ..
*     .. External Functions ..
      DOUBLE PRECISION   DZNRM2
      LOGICAL            LSAME
      EXTERNAL           DZNRM2, LSAME
*     ..
*     .. Intrinsic Functions
      INTRINSIC          ATAN2, COS, MAX, MIN, SIN
      INTRINSIC          DCMPLX, DCONJG
*     ..
*     .. Executable Statements ..
*
*     Test input arguments
*
      INFO = 0
      COLMAJOR = .NOT. LSAME( TRANS, 'T' )
      IF( .NOT. LSAME( SIGNS, 'O' ) ) THEN
         Z1 = REALONE
         Z2 = REALONE
         Z3 = REALONE
         Z4 = REALONE
      ELSE
         Z1 = REALONE
         Z2 = -REALONE
         Z3 = REALONE
         Z4 = -REALONE
      END IF
      LQUERY = LWORK .EQ. -1
*
      IF( M .LT. 0 ) THEN
         INFO = -3
      ELSE IF( P .LT. 0 .OR. P .GT. M ) THEN
         INFO = -4
      ELSE IF( Q .LT. 0 .OR. Q .GT. P .OR. Q .GT. M-P .OR.
     $         Q .GT. M-Q ) THEN
         INFO = -5
      ELSE IF( COLMAJOR .AND. LDX11 .LT. MAX( 1, P ) ) THEN
         INFO = -7
      ELSE IF( .NOT.COLMAJOR .AND. LDX11 .LT. MAX( 1, Q ) ) THEN
         INFO = -7
      ELSE IF( COLMAJOR .AND. LDX12 .LT. MAX( 1, P ) ) THEN
         INFO = -9
      ELSE IF( .NOT.COLMAJOR .AND. LDX12 .LT. MAX( 1, M-Q ) ) THEN
         INFO = -9
      ELSE IF( COLMAJOR .AND. LDX21 .LT. MAX( 1, M-P ) ) THEN
         INFO = -11
      ELSE IF( .NOT.COLMAJOR .AND. LDX21 .LT. MAX( 1, Q ) ) THEN
         INFO = -11
      ELSE IF( COLMAJOR .AND. LDX22 .LT. MAX( 1, M-P ) ) THEN
         INFO = -13
      ELSE IF( .NOT.COLMAJOR .AND. LDX22 .LT. MAX( 1, M-Q ) ) THEN
         INFO = -13
      END IF
*
*     Compute workspace
*
      IF( INFO .EQ. 0 ) THEN
         LWORKOPT = M - Q
         LWORKMIN = M - Q
         WORK(1) = LWORKOPT
         IF( LWORK .LT. LWORKMIN .AND. .NOT. LQUERY ) THEN
            INFO = -21
         END IF
      END IF
      IF( INFO .NE. 0 ) THEN
         CALL XERBLA( 'xORBDB', -INFO )
         RETURN
      ELSE IF( LQUERY ) THEN
         RETURN
      END IF
*
*     Handle column-major and row-major separately
*
      IF( COLMAJOR ) THEN
*
*        Reduce columns 1, ..., Q of X11, X12, X21, and X22 
*
         DO I = 1, Q
*
            IF( I .EQ. 1 ) THEN
               CALL ZSCAL( P-I+1, DCMPLX( Z1, 0.0D0 ), X11(I,I), 1 )
            ELSE
               CALL ZSCAL( P-I+1, DCMPLX( Z1*COS(PHI(I-1)), 0.0D0 ),
     $                     X11(I,I), 1 )
               CALL ZAXPY( P-I+1, DCMPLX( -Z1*Z3*Z4*SIN(PHI(I-1)),
     $                     0.0D0 ), X12(I,I-1), 1, X11(I,I), 1 )
            END IF
            IF( I .EQ. 1 ) THEN
               CALL ZSCAL( M-P-I+1, DCMPLX( Z2, 0.0D0 ), X21(I,I), 1 )
            ELSE
               CALL ZSCAL( M-P-I+1, DCMPLX( Z2*COS(PHI(I-1)), 0.0D0 ),
     $                     X21(I,I), 1 )
               CALL ZAXPY( M-P-I+1, DCMPLX( -Z2*Z3*Z4*SIN(PHI(I-1)),
     $                     0.0D0 ), X22(I,I-1), 1, X21(I,I), 1 )
            END IF
*
            THETA(I) = ATAN2( DZNRM2( M-P-I+1, X21(I,I), 1 ),
     $                 DZNRM2( P-I+1, X11(I,I), 1 ) )
*
            CALL ZLARFGP( P-I+1, X11(I,I), X11(I+1,I), 1, TAUP1(I) )
            X11(I,I) = ONE
            CALL ZLARFGP( M-P-I+1, X21(I,I), X21(I+1,I), 1, TAUP2(I) )
            X21(I,I) = ONE
*
            CALL ZLARF( 'L', P-I+1, Q-I, X11(I,I), 1, DCONJG(TAUP1(I)),
     $                  X11(I,I+1), LDX11, WORK )
            CALL ZLARF( 'L', P-I+1, M-Q-I+1, X11(I,I), 1,
     $                  DCONJG(TAUP1(I)), X12(I,I), LDX12, WORK )
            CALL ZLARF( 'L', M-P-I+1, Q-I, X21(I,I), 1,
     $                  DCONJG(TAUP2(I)), X21(I,I+1), LDX21, WORK )
            CALL ZLARF( 'L', M-P-I+1, M-Q-I+1, X21(I,I), 1,
     $                  DCONJG(TAUP2(I)), X22(I,I), LDX22, WORK )
*
            IF( I .LT. Q ) THEN
               CALL ZSCAL( Q-I, DCMPLX( -Z1*Z3*SIN(THETA(I)), 0.0D0 ),
     $                     X11(I,I+1), LDX11 )
               CALL ZAXPY( Q-I, DCMPLX( Z2*Z3*COS(THETA(I)), 0.0D0 ),
     $                     X21(I,I+1), LDX21, X11(I,I+1), LDX11 )
            END IF
            CALL ZSCAL( M-Q-I+1, DCMPLX( -Z1*Z4*SIN(THETA(I)), 0.0D0 ),
     $                  X12(I,I), LDX12 )
            CALL ZAXPY( M-Q-I+1, DCMPLX( Z2*Z4*COS(THETA(I)), 0.0D0 ),
     $                  X22(I,I), LDX22, X12(I,I), LDX12 )
*
            IF( I .LT. Q )
     $         PHI(I) = ATAN2( DZNRM2( Q-I, X11(I,I+1), LDX11 ),
     $                  DZNRM2( M-Q-I+1, X12(I,I), LDX12 ) )
*
            IF( I .LT. Q ) THEN
               CALL ZLACGV( Q-I, X11(I,I+1), LDX11 )
               CALL ZLARFGP( Q-I, X11(I,I+1), X11(I,I+2), LDX11,
     $                       TAUQ1(I) )
               X11(I,I+1) = ONE
            END IF
            CALL ZLACGV( M-Q-I+1, X12(I,I), LDX12 )
            CALL ZLARFGP( M-Q-I+1, X12(I,I), X12(I,I+1), LDX12,
     $                    TAUQ2(I) )
            X12(I,I) = ONE
*
            IF( I .LT. Q ) THEN
               CALL ZLARF( 'R', P-I, Q-I, X11(I,I+1), LDX11, TAUQ1(I),
     $                     X11(I+1,I+1), LDX11, WORK )
               CALL ZLARF( 'R', M-P-I, Q-I, X11(I,I+1), LDX11, TAUQ1(I),
     $                     X21(I+1,I+1), LDX21, WORK )
            END IF
            CALL ZLARF( 'R', P-I, M-Q-I+1, X12(I,I), LDX12, TAUQ2(I),
     $                  X12(I+1,I), LDX12, WORK )
            CALL ZLARF( 'R', M-P-I, M-Q-I+1, X12(I,I), LDX12, TAUQ2(I),
     $                  X22(I+1,I), LDX22, WORK )
*
            IF( I .LT. Q )
     $         CALL ZLACGV( Q-I, X11(I,I+1), LDX11 )
            CALL ZLACGV( M-Q-I+1, X12(I,I), LDX12 )
*
         END DO
*
*        Reduce columns Q + 1, ..., P of X12, X22
*
         DO I = Q + 1, P
*
            CALL ZSCAL( M-Q-I+1, DCMPLX( -Z1*Z4, 0.0D0 ), X12(I,I),
     $                  LDX12 )
            CALL ZLACGV( M-Q-I+1, X12(I,I), LDX12 )
            CALL ZLARFGP( M-Q-I+1, X12(I,I), X12(I,I+1), LDX12,
     $                    TAUQ2(I) )
            X12(I,I) = ONE
*
            CALL ZLARF( 'R', P-I, M-Q-I+1, X12(I,I), LDX12, TAUQ2(I),
     $                  X12(I+1,I), LDX12, WORK )
            IF( M-P-Q .GE. 1 )
     $         CALL ZLARF( 'R', M-P-Q, M-Q-I+1, X12(I,I), LDX12,
     $                     TAUQ2(I), X22(Q+1,I), LDX22, WORK )
*
            CALL ZLACGV( M-Q-I+1, X12(I,I), LDX12 )
*
         END DO
*
*        Reduce columns P + 1, ..., M - Q of X12, X22
*
         DO I = 1, M - P - Q
*
            CALL ZSCAL( M-P-Q-I+1, DCMPLX( Z2*Z4, 0.0D0 ),
     $                  X22(Q+I,P+I), LDX22 )
            CALL ZLACGV( M-P-Q-I+1, X22(Q+I,P+I), LDX22 )
            CALL ZLARFGP( M-P-Q-I+1, X22(Q+I,P+I), X22(Q+I,P+I+1),
     $                    LDX22, TAUQ2(P+I) )
            X22(Q+I,P+I) = ONE
            CALL ZLARF( 'R', M-P-Q-I, M-P-Q-I+1, X22(Q+I,P+I), LDX22,
     $                  TAUQ2(P+I), X22(Q+I+1,P+I), LDX22, WORK )
*
            CALL ZLACGV( M-P-Q-I+1, X22(Q+I,P+I), LDX22 )
*
         END DO
*
      ELSE
*
*        Reduce columns 1, ..., Q of X11, X12, X21, X22
*
         DO I = 1, Q
*
            IF( I .EQ. 1 ) THEN
               CALL ZSCAL( P-I+1, DCMPLX( Z1, 0.0D0 ), X11(I,I),
     $                     LDX11 )
            ELSE
               CALL ZSCAL( P-I+1, DCMPLX( Z1*COS(PHI(I-1)), 0.0D0 ),
     $                     X11(I,I), LDX11 )
               CALL ZAXPY( P-I+1, DCMPLX( -Z1*Z3*Z4*SIN(PHI(I-1)),
     $                     0.0D0 ), X12(I-1,I), LDX12, X11(I,I), LDX11 )
            END IF
            IF( I .EQ. 1 ) THEN
               CALL ZSCAL( M-P-I+1, DCMPLX( Z2, 0.0D0 ), X21(I,I),
     $                     LDX21 )
            ELSE
               CALL ZSCAL( M-P-I+1, DCMPLX( Z2*COS(PHI(I-1)), 0.0D0 ),
     $                     X21(I,I), LDX21 )
               CALL ZAXPY( M-P-I+1, DCMPLX( -Z2*Z3*Z4*SIN(PHI(I-1)),
     $                     0.0D0 ), X22(I-1,I), LDX22, X21(I,I), LDX21 )
            END IF
*
            THETA(I) = ATAN2( DZNRM2( M-P-I+1, X21(I,I), LDX21 ),
     $                 DZNRM2( P-I+1, X11(I,I), LDX11 ) )
*
            CALL ZLACGV( P-I+1, X11(I,I), LDX11 )
            CALL ZLACGV( M-P-I+1, X21(I,I), LDX21 )
*
            CALL ZLARFGP( P-I+1, X11(I,I), X11(I,I+1), LDX11, TAUP1(I) )
            X11(I,I) = ONE
            CALL ZLARFGP( M-P-I+1, X21(I,I), X21(I,I+1), LDX21,
     $                    TAUP2(I) )
            X21(I,I) = ONE
*
            CALL ZLARF( 'R', Q-I, P-I+1, X11(I,I), LDX11, TAUP1(I),
     $                  X11(I+1,I), LDX11, WORK )
            CALL ZLARF( 'R', M-Q-I+1, P-I+1, X11(I,I), LDX11, TAUP1(I),
     $                  X12(I,I), LDX12, WORK )
            CALL ZLARF( 'R', Q-I, M-P-I+1, X21(I,I), LDX21, TAUP2(I),
     $                  X21(I+1,I), LDX21, WORK )
            CALL ZLARF( 'R', M-Q-I+1, M-P-I+1, X21(I,I), LDX21,
     $                  TAUP2(I), X22(I,I), LDX22, WORK )
*
            CALL ZLACGV( P-I+1, X11(I,I), LDX11 )
            CALL ZLACGV( M-P-I+1, X21(I,I), LDX21 )
*
            IF( I .LT. Q ) THEN
               CALL ZSCAL( Q-I, DCMPLX( -Z1*Z3*SIN(THETA(I)), 0.0D0 ),
     $                     X11(I+1,I), 1 )
               CALL ZAXPY( Q-I, DCMPLX( Z2*Z3*COS(THETA(I)), 0.0D0 ),
     $                     X21(I+1,I), 1, X11(I+1,I), 1 )
            END IF
            CALL ZSCAL( M-Q-I+1, DCMPLX( -Z1*Z4*SIN(THETA(I)), 0.0D0 ),
     $                  X12(I,I), 1 )
            CALL ZAXPY( M-Q-I+1, DCMPLX( Z2*Z4*COS(THETA(I)), 0.0D0 ),
     $                  X22(I,I), 1, X12(I,I), 1 )
*
            IF( I .LT. Q )
     $         PHI(I) = ATAN2( DZNRM2( Q-I, X11(I+1,I), 1 ),
     $                  DZNRM2( M-Q-I+1, X12(I,I), 1 ) )
*
            IF( I .LT. Q ) THEN
               CALL ZLARFGP( Q-I, X11(I+1,I), X11(I+2,I), 1, TAUQ1(I) )
               X11(I+1,I) = ONE
            END IF
            CALL ZLARFGP( M-Q-I+1, X12(I,I), X12(I+1,I), 1, TAUQ2(I) )
            X12(I,I) = ONE
*
            IF( I .LT. Q ) THEN
               CALL ZLARF( 'L', Q-I, P-I, X11(I+1,I), 1,
     $                     DCONJG(TAUQ1(I)), X11(I+1,I+1), LDX11, WORK )
               CALL ZLARF( 'L', Q-I, M-P-I, X11(I+1,I), 1,
     $                     DCONJG(TAUQ1(I)), X21(I+1,I+1), LDX21, WORK )
            END IF
            CALL ZLARF( 'L', M-Q-I+1, P-I, X12(I,I), 1,
     $                  DCONJG(TAUQ2(I)), X12(I,I+1), LDX12, WORK )
            CALL ZLARF( 'L', M-Q-I+1, M-P-I, X12(I,I), 1,
     $                  DCONJG(TAUQ2(I)), X22(I,I+1), LDX22, WORK )
*
         END DO
*
*        Reduce columns Q + 1, ..., P of X12, X22
*
         DO I = Q + 1, P
*
            CALL ZSCAL( M-Q-I+1, DCMPLX( -Z1*Z4, 0.0D0 ), X12(I,I), 1 )
            CALL ZLARFGP( M-Q-I+1, X12(I,I), X12(I+1,I), 1, TAUQ2(I) )
            X12(I,I) = ONE
*
            CALL ZLARF( 'L', M-Q-I+1, P-I, X12(I,I), 1,
     $                  DCONJG(TAUQ2(I)), X12(I,I+1), LDX12, WORK )
            IF( M-P-Q .GE. 1 )
     $         CALL ZLARF( 'L', M-Q-I+1, M-P-Q, X12(I,I), 1,
     $                     DCONJG(TAUQ2(I)), X22(I,Q+1), LDX22, WORK )
*
         END DO
*
*        Reduce columns P + 1, ..., M - Q of X12, X22
*
         DO I = 1, M - P - Q
*
            CALL ZSCAL( M-P-Q-I+1, DCMPLX( Z2*Z4, 0.0D0 ),
     $                  X22(P+I,Q+I), 1 )
            CALL ZLARFGP( M-P-Q-I+1, X22(P+I,Q+I), X22(P+I+1,Q+I), 1,
     $                    TAUQ2(P+I) )
            X22(P+I,Q+I) = ONE
*
            CALL ZLARF( 'L', M-P-Q-I+1, M-P-Q-I, X22(P+I,Q+I), 1,
     $                  DCONJG(TAUQ2(P+I)), X22(P+I,Q+I+1), LDX22,
     $                  WORK )
*
         END DO
*
      END IF
*
      RETURN
*
*     End of ZUNBDB
*
      END