zuncsd2by1.f

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*> \brief \b ZUNCSD2BY1
*
*  =========== DOCUMENTATION ===========
*
* Online html documentation available at
*            http://www.netlib.org/lapack/explore-html/
*
*> \htmlonly
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*> \endhtmlonly
*
*  Definition:
*  ===========
*
*       SUBROUTINE ZUNCSD2BY1( JOBU1, JOBU2, JOBV1T, M, P, Q, X11, LDX11,
*                              X21, LDX21, THETA, U1, LDU1, U2, LDU2, V1T,
*                              LDV1T, WORK, LWORK, RWORK, LRWORK, IWORK,
*                              INFO )
*
*       .. Scalar Arguments ..
*       CHARACTER          JOBU1, JOBU2, JOBV1T
*       INTEGER            INFO, LDU1, LDU2, LDV1T, LWORK, LDX11, LDX21,
*      $                   M, P, Q
*       INTEGER            LRWORK, LRWORKMIN, LRWORKOPT
*       ..
*       .. Array Arguments ..
*       DOUBLE PRECISION   RWORK(*)
*       DOUBLE PRECISION   THETA(*)
*       COMPLEX*16         U1(LDU1,*), U2(LDU2,*), V1T(LDV1T,*), WORK(*),
*      $                   X11(LDX11,*), X21(LDX21,*)
*       INTEGER            IWORK(*)
*       ..
*
*
*> \par Purpose:
*  =============
*>
*>\verbatim
*>
*> ZUNCSD2BY1 computes the CS decomposition of an M-by-Q matrix X with
*> orthonormal columns that has been partitioned into a 2-by-1 block
*> structure:
*>
*>                                [  I1 0  0 ]
*>                                [  0  C  0 ]
*>          [ X11 ]   [ U1 |    ] [  0  0  0 ]
*>      X = [-----] = [---------] [----------] V1**T .
*>          [ X21 ]   [    | U2 ] [  0  0  0 ]
*>                                [  0  S  0 ]
*>                                [  0  0  I2]
*>
*> X11 is P-by-Q. The unitary matrices U1, U2, and V1 are P-by-P,
*> (M-P)-by-(M-P), and Q-by-Q, respectively. C and S are R-by-R
*> nonnegative diagonal matrices satisfying C^2 + S^2 = I, in which
*> R = MIN(P,M-P,Q,M-Q). I1 is a K1-by-K1 identity matrix and I2 is a
*> K2-by-K2 identity matrix, where K1 = MAX(Q+P-M,0), K2 = MAX(Q-P,0).
*> \endverbatim
*
*  Arguments:
*  ==========
*
*> \param[in] JOBU1
*> \verbatim
*>          JOBU1 is CHARACTER
*>          = 'Y':      U1 is computed;
*>          otherwise:  U1 is not computed.
*> \endverbatim
*>
*> \param[in] JOBU2
*> \verbatim
*>          JOBU2 is CHARACTER
*>          = 'Y':      U2 is computed;
*>          otherwise:  U2 is not computed.
*> \endverbatim
*>
*> \param[in] JOBV1T
*> \verbatim
*>          JOBV1T is CHARACTER
*>          = 'Y':      V1T is computed;
*>          otherwise:  V1T is not computed.
*> \endverbatim
*>
*> \param[in] M
*> \verbatim
*>          M is INTEGER
*>          The number of rows in X.
*> \endverbatim
*>
*> \param[in] P
*> \verbatim
*>          P is INTEGER
*>          The number of rows in X11. 0 <= P <= M.
*> \endverbatim
*>
*> \param[in] Q
*> \verbatim
*>          Q is INTEGER
*>          The number of columns in X11 and X21. 0 <= Q <= M.
*> \endverbatim
*>
*> \param[in,out] X11
*> \verbatim
*>          X11 is COMPLEX*16 array, dimension (LDX11,Q)
*>          On entry, part of the unitary matrix whose CSD is desired.
*> \endverbatim
*>
*> \param[in] LDX11
*> \verbatim
*>          LDX11 is INTEGER
*>          The leading dimension of X11. LDX11 >= MAX(1,P).
*> \endverbatim
*>
*> \param[in,out] X21
*> \verbatim
*>          X21 is COMPLEX*16 array, dimension (LDX21,Q)
*>          On entry, part of the unitary matrix whose CSD is desired.
*> \endverbatim
*>
*> \param[in] LDX21
*> \verbatim
*>          LDX21 is INTEGER
*>          The leading dimension of X21. LDX21 >= MAX(1,M-P).
*> \endverbatim
*>
*> \param[out] THETA
*> \verbatim
*>          THETA is DOUBLE PRECISION array, dimension (R), in which R =
*>          MIN(P,M-P,Q,M-Q).
*>          C = DIAG( COS(THETA(1)), ... , COS(THETA(R)) ) and
*>          S = DIAG( SIN(THETA(1)), ... , SIN(THETA(R)) ).
*> \endverbatim
*>
*> \param[out] U1
*> \verbatim
*>          U1 is COMPLEX*16 array, dimension (P)
*>          If JOBU1 = 'Y', U1 contains the P-by-P unitary matrix U1.
*> \endverbatim
*>
*> \param[in] LDU1
*> \verbatim
*>          LDU1 is INTEGER
*>          The leading dimension of U1. If JOBU1 = 'Y', LDU1 >=
*>          MAX(1,P).
*> \endverbatim
*>
*> \param[out] U2
*> \verbatim
*>          U2 is COMPLEX*16 array, dimension (M-P)
*>          If JOBU2 = 'Y', U2 contains the (M-P)-by-(M-P) unitary
*>          matrix U2.
*> \endverbatim
*>
*> \param[in] LDU2
*> \verbatim
*>          LDU2 is INTEGER
*>          The leading dimension of U2. If JOBU2 = 'Y', LDU2 >=
*>          MAX(1,M-P).
*> \endverbatim
*>
*> \param[out] V1T
*> \verbatim
*>          V1T is COMPLEX*16 array, dimension (Q)
*>          If JOBV1T = 'Y', V1T contains the Q-by-Q matrix unitary
*>          matrix V1**T.
*> \endverbatim
*>
*> \param[in] LDV1T
*> \verbatim
*>          LDV1T is INTEGER
*>          The leading dimension of V1T. If JOBV1T = 'Y', LDV1T >=
*>          MAX(1,Q).
*> \endverbatim
*>
*> \param[out] WORK
*> \verbatim
*>          WORK is COMPLEX*16 array, dimension (MAX(1,LWORK))
*>          On exit, if INFO = 0, WORK(1) returns the optimal LWORK.
*> \endverbatim
*>
*> \param[in] LWORK
*> \verbatim
*>          LWORK is INTEGER
*>          The dimension of the array WORK.
*>
*>          If LWORK = -1, then a workspace query is assumed; the routine
*>          only calculates the optimal size of the WORK and RWORK
*>          arrays, returns this value as the first entry of the WORK
*>          and RWORK array, respectively, and no error message related
*>          to LWORK or LRWORK is issued by XERBLA.
*> \endverbatim
*>
*> \param[out] RWORK
*> \verbatim
*>          RWORK is DOUBLE PRECISION array, dimension (MAX(1,LRWORK))
*>          On exit, if INFO = 0, RWORK(1) returns the optimal LRWORK.
*>          If INFO > 0 on exit, RWORK(2:R) contains the values PHI(1),
*>          ..., PHI(R-1) that, together with THETA(1), ..., THETA(R),
*>          define the matrix in intermediate bidiagonal-block form
*>          remaining after nonconvergence. INFO specifies the number
*>          of nonzero PHI's.
*> \endverbatim
*>
*> \param[in] LRWORK
*> \verbatim
*>          LRWORK is INTEGER
*>          The dimension of the array RWORK.
*>
*>          If LRWORK=-1, then a workspace query is assumed; the routine
*>          only calculates the optimal size of the WORK and RWORK
*>          arrays, returns this value as the first entry of the WORK
*>          and RWORK array, respectively, and no error message related
*>          to LWORK or LRWORK is issued by XERBLA.
*> \endverbatim
*
*> \param[out] IWORK
*> \verbatim
*>          IWORK is INTEGER array, dimension (M-MIN(P,M-P,Q,M-Q))
*> \endverbatim
*>
*> \param[out] INFO
*> \verbatim
*>          INFO is INTEGER
*>          = 0:  successful exit.
*>          < 0:  if INFO = -i, the i-th argument had an illegal value.
*>          > 0:  ZBBCSD did not converge. See the description of WORK
*>                above for details.
*> \endverbatim
*
*> \par References:
*  ================
*>
*>  [1] Brian D. Sutton. Computing the complete CS decomposition. Numer.
*>      Algorithms, 50(1):33-65, 2009.
*
*  Authors:
*  ========
*
*> \author Univ. of Tennessee
*> \author Univ. of California Berkeley
*> \author Univ. of Colorado Denver
*> \author NAG Ltd.
*
*> \ingroup complex16OTHERcomputational
*
*  =====================================================================
      SUBROUTINE zuncsd2by1( JOBU1, JOBU2, JOBV1T, M, P, Q, X11, LDX11,
     $                       X21, LDX21, THETA, U1, LDU1, U2, LDU2, V1T,
     $                       LDV1T, WORK, LWORK, RWORK, LRWORK, IWORK,
     $                       INFO )
*
*  -- LAPACK computational routine --
*  -- LAPACK is a software package provided by Univ. of Tennessee,    --
*  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
*
*     .. Scalar Arguments ..
      CHARACTER          JOBU1, JOBU2, JOBV1T
      INTEGER            INFO, LDU1, LDU2, LDV1T, LWORK, LDX11, LDX21,
     $                   M, P, Q
      INTEGER            LRWORK, LRWORKMIN, LRWORKOPT
*     ..
*     .. Array Arguments ..
      DOUBLE PRECISION   RWORK(*)
      DOUBLE PRECISION   THETA(*)
      COMPLEX*16         U1(LDU1,*), U2(LDU2,*), V1T(LDV1T,*), WORK(*),
     $                   x11(ldx11,*), x21(ldx21,*)
      INTEGER            IWORK(*)
*     ..
*
*  =====================================================================
*
*     .. Parameters ..
      COMPLEX*16         ONE, ZERO
      PARAMETER          ( ONE = (1.0d0,0.0d0), zero = (0.0d0,0.0d0) )
*     ..
*     .. Local Scalars ..
      INTEGER            CHILDINFO, I, IB11D, IB11E, IB12D, IB12E,
     $                   IB21D, IB21E, IB22D, IB22E, IBBCSD, IORBDB,
     $                   IORGLQ, IORGQR, IPHI, ITAUP1, ITAUP2, ITAUQ1,
     $                   j, lbbcsd, lorbdb, lorglq, lorglqmin,
     $                   lorglqopt, lorgqr, lorgqrmin, lorgqropt,
     $                   lworkmin, lworkopt, r
      LOGICAL            LQUERY, WANTU1, WANTU2, WANTV1T
*     ..
*     .. Local Arrays ..
      DOUBLE PRECISION   DUM( 1 )
      COMPLEX*16         CDUM( 1, 1 )
*     ..
*     .. External Subroutines ..
      EXTERNAL           zbbcsd, zcopy, zlacpy, zlapmr, zlapmt, zunbdb1,
     $                   zunbdb2, zunbdb3, zunbdb4, zunglq, zungqr,
     $                   xerbla
*     ..
*     .. External Functions ..
      LOGICAL            LSAME
      EXTERNAL           LSAME
*     ..
*     .. Intrinsic Function ..
      INTRINSIC          int, max, min
*     ..
*     .. Executable Statements ..
*
*     Test input arguments
*
      info = 0
      wantu1 = lsame( jobu1, 'Y' )
      wantu2 = lsame( jobu2, 'Y' )
      wantv1t = lsame( jobv1t, 'Y' )
      lquery = ( lwork.EQ.-1 ) .OR. ( lrwork.EQ.-1 )
*
      IF( m .LT. 0 ) THEN
         info = -4
      ELSE IF( p .LT. 0 .OR. p .GT. m ) THEN
         info = -5
      ELSE IF( q .LT. 0 .OR. q .GT. m ) THEN
         info = -6
      ELSE IF( ldx11 .LT. max( 1, p ) ) THEN
         info = -8
      ELSE IF( ldx21 .LT. max( 1, m-p ) ) THEN
         info = -10
      ELSE IF( wantu1 .AND. ldu1 .LT. max( 1, p ) ) THEN
         info = -13
      ELSE IF( wantu2 .AND. ldu2 .LT. max( 1, m - p ) ) THEN
         info = -15
      ELSE IF( wantv1t .AND. ldv1t .LT. max( 1, q ) ) THEN
         info = -17
      END IF
*
      r = min( p, m-p, q, m-q )
*
*     Compute workspace
*
*       WORK layout:
*     |-----------------------------------------|
*     | LWORKOPT (1)                            |
*     |-----------------------------------------|
*     | TAUP1 (MAX(1,P))                        |
*     | TAUP2 (MAX(1,M-P))                      |
*     | TAUQ1 (MAX(1,Q))                        |
*     |-----------------------------------------|
*     | ZUNBDB WORK | ZUNGQR WORK | ZUNGLQ WORK |
*     |             |             |             |
*     |             |             |             |
*     |             |             |             |
*     |             |             |             |
*     |-----------------------------------------|
*       RWORK layout:
*     |------------------|
*     | LRWORKOPT (1)    |
*     |------------------|
*     | PHI (MAX(1,R-1)) |
*     |------------------|
*     | B11D (R)         |
*     | B11E (R-1)       |
*     | B12D (R)         |
*     | B12E (R-1)       |
*     | B21D (R)         |
*     | B21E (R-1)       |
*     | B22D (R)         |
*     | B22E (R-1)       |
*     | ZBBCSD RWORK     |
*     |------------------|
*
      IF( info .EQ. 0 ) THEN
         iphi = 2
         ib11d = iphi + max( 1, r-1 )
         ib11e = ib11d + max( 1, r )
         ib12d = ib11e + max( 1, r - 1 )
         ib12e = ib12d + max( 1, r )
         ib21d = ib12e + max( 1, r - 1 )
         ib21e = ib21d + max( 1, r )
         ib22d = ib21e + max( 1, r - 1 )
         ib22e = ib22d + max( 1, r )
         ibbcsd = ib22e + max( 1, r - 1 )
         itaup1 = 2
         itaup2 = itaup1 + max( 1, p )
         itauq1 = itaup2 + max( 1, m-p )
         iorbdb = itauq1 + max( 1, q )
         iorgqr = itauq1 + max( 1, q )
         iorglq = itauq1 + max( 1, q )
         lorgqrmin = 1
         lorgqropt = 1
         lorglqmin = 1
         lorglqopt = 1
         IF( r .EQ. q ) THEN
            CALL zunbdb1( m, p, q, x11, ldx11, x21, ldx21, theta, dum,
     $                    cdum, cdum, cdum, work, -1, childinfo )
            lorbdb = int( work(1) )
            IF( wantu1 .AND. p .GT. 0 ) THEN
               CALL zungqr( p, p, q, u1, ldu1, cdum, work(1), -1,
     $                      childinfo )
               lorgqrmin = max( lorgqrmin, p )
               lorgqropt = max( lorgqropt, int( work(1) ) )
            ENDIF
            IF( wantu2 .AND. m-p .GT. 0 ) THEN
               CALL zungqr( m-p, m-p, q, u2, ldu2, cdum, work(1), -1,
     $                      childinfo )
               lorgqrmin = max( lorgqrmin, m-p )
               lorgqropt = max( lorgqropt, int( work(1) ) )
            END IF
            IF( wantv1t .AND. q .GT. 0 ) THEN
               CALL zunglq( q-1, q-1, q-1, v1t, ldv1t,
     $                      cdum, work(1), -1, childinfo )
               lorglqmin = max( lorglqmin, q-1 )
               lorglqopt = max( lorglqopt, int( work(1) ) )
            END IF
            CALL zbbcsd( jobu1, jobu2, jobv1t, 'N', 'N', m, p, q, theta,
     $                   dum, u1, ldu1, u2, ldu2, v1t, ldv1t, cdum, 1,
     $                   dum, dum, dum, dum, dum, dum, dum, dum,
     $                   rwork(1), -1, childinfo )
            lbbcsd = int( rwork(1) )
         ELSE IF( r .EQ. p ) THEN
            CALL zunbdb2( m, p, q, x11, ldx11, x21, ldx21, theta, dum,
     $                    cdum, cdum, cdum, work(1), -1, childinfo )
            lorbdb = int( work(1) )
            IF( wantu1 .AND. p .GT. 0 ) THEN
               CALL zungqr( p-1, p-1, p-1, u1(2,2), ldu1, cdum, work(1),
     $                      -1, childinfo )
               lorgqrmin = max( lorgqrmin, p-1 )
               lorgqropt = max( lorgqropt, int( work(1) ) )
            END IF
            IF( wantu2 .AND. m-p .GT. 0 ) THEN
               CALL zungqr( m-p, m-p, q, u2, ldu2, cdum, work(1), -1,
     $                      childinfo )
               lorgqrmin = max( lorgqrmin, m-p )
               lorgqropt = max( lorgqropt, int( work(1) ) )
            END IF
            IF( wantv1t .AND. q .GT. 0 ) THEN
               CALL zunglq( q, q, r, v1t, ldv1t, cdum, work(1), -1,
     $                      childinfo )
               lorglqmin = max( lorglqmin, q )
               lorglqopt = max( lorglqopt, int( work(1) ) )
            END IF
            CALL zbbcsd( jobv1t, 'N', jobu1, jobu2, 'T', m, q, p, theta,
     $                   dum, v1t, ldv1t, cdum, 1, u1, ldu1, u2, ldu2,
     $                   dum, dum, dum, dum, dum, dum, dum, dum,
     $                   rwork(1), -1, childinfo )
            lbbcsd = int( rwork(1) )
         ELSE IF( r .EQ. m-p ) THEN
            CALL zunbdb3( m, p, q, x11, ldx11, x21, ldx21, theta, dum,
     $                    cdum, cdum, cdum, work(1), -1, childinfo )
            lorbdb = int( work(1) )
            IF( wantu1 .AND. p .GT. 0 ) THEN
               CALL zungqr( p, p, q, u1, ldu1, cdum, work(1), -1,
     $                      childinfo )
               lorgqrmin = max( lorgqrmin, p )
               lorgqropt = max( lorgqropt, int( work(1) ) )
            END IF
            IF( wantu2 .AND. m-p .GT. 0 ) THEN
               CALL zungqr( m-p-1, m-p-1, m-p-1, u2(2,2), ldu2, cdum,
     $                      work(1), -1, childinfo )
               lorgqrmin = max( lorgqrmin, m-p-1 )
               lorgqropt = max( lorgqropt, int( work(1) ) )
            END IF
            IF( wantv1t .AND. q .GT. 0 ) THEN
               CALL zunglq( q, q, r, v1t, ldv1t, cdum, work(1), -1,
     $                      childinfo )
               lorglqmin = max( lorglqmin, q )
               lorglqopt = max( lorglqopt, int( work(1) ) )
            END IF
            CALL zbbcsd( 'n', JOBV1T, JOBU2, JOBU1, 't', M, M-Q, M-P,
     $                   THETA, DUM, CDUM, 1, V1T, LDV1T, U2, LDU2, U1,
     $                   LDU1, DUM, DUM, DUM, DUM, DUM, DUM, DUM, DUM,
     $                   RWORK(1), -1, CHILDINFO )
            LBBCSD = INT( RWORK(1) )
         ELSE
            CALL ZUNBDB4( M, P, Q, X11, LDX11, X21, LDX21, THETA, DUM,
     $                    CDUM, CDUM, CDUM, CDUM, WORK(1), -1, CHILDINFO
     $                  )
            LORBDB = M + INT( WORK(1) )
.AND..GT.            IF( WANTU1  P  0 ) THEN
               CALL ZUNGQR( P, P, M-Q, U1, LDU1, CDUM, WORK(1), -1,
     $                      CHILDINFO )
               LORGQRMIN = MAX( LORGQRMIN, P )
               LORGQROPT = MAX( LORGQROPT, INT( WORK(1) ) )
            END IF
.AND..GT.            IF( WANTU2  M-P  0 ) THEN
               CALL ZUNGQR( M-P, M-P, M-Q, U2, LDU2, CDUM, WORK(1), -1,
     $                      CHILDINFO )
               LORGQRMIN = MAX( LORGQRMIN, M-P )
               LORGQROPT = MAX( LORGQROPT, INT( WORK(1) ) )
            END IF
.AND..GT.            IF( WANTV1T  Q  0 ) THEN
               CALL ZUNGLQ( Q, Q, Q, V1T, LDV1T, CDUM, WORK(1), -1,
     $                      CHILDINFO )
               LORGLQMIN = MAX( LORGLQMIN, Q )
               LORGLQOPT = MAX( LORGLQOPT, INT( WORK(1) ) )
            END IF
            CALL ZBBCSD( JOBU2, JOBU1, 'n', JOBV1T, 'n', M, M-P, M-Q,
     $                   THETA, DUM, U2, LDU2, U1, LDU1, CDUM, 1, V1T,
     $                   LDV1T, DUM, DUM, DUM, DUM, DUM, DUM, DUM, DUM,
     $                   RWORK(1), -1, CHILDINFO )
            LBBCSD = INT( RWORK(1) )
         END IF
         LRWORKMIN = IBBCSD+LBBCSD-1
         LRWORKOPT = LRWORKMIN
         RWORK(1) = LRWORKOPT
         LWORKMIN = MAX( IORBDB+LORBDB-1,
     $                   IORGQR+LORGQRMIN-1,
     $                   IORGLQ+LORGLQMIN-1 )
         LWORKOPT = MAX( IORBDB+LORBDB-1,
     $                   IORGQR+LORGQROPT-1,
     $                   IORGLQ+LORGLQOPT-1 )
         WORK(1) = LWORKOPT
.LT..AND..NOT.         IF( LWORK  LWORKMIN  LQUERY ) THEN
            INFO = -19
         END IF
.LT..AND..NOT.         IF( LRWORK  LRWORKMIN  LQUERY ) THEN
            INFO = -21
         END IF
      END IF
.NE.      IF( INFO  0 ) THEN
         CALL XERBLA( 'zuncsd2by1', -INFO )
         RETURN
      ELSE IF( LQUERY ) THEN
         RETURN
      END IF
      LORGQR = LWORK-IORGQR+1
      LORGLQ = LWORK-IORGLQ+1
*
*     Handle four cases separately: R = Q, R = P, R = M-P, and R = M-Q,
*     in which R = MIN(P,M-P,Q,M-Q)
*
.EQ.      IF( R  Q ) THEN
*
*        Case 1: R = Q
*
*        Simultaneously bidiagonalize X11 and X21
*
         CALL ZUNBDB1( M, P, Q, X11, LDX11, X21, LDX21, THETA,
     $                 RWORK(IPHI), WORK(ITAUP1), WORK(ITAUP2),
     $                 WORK(ITAUQ1), WORK(IORBDB), LORBDB, CHILDINFO )
*
*        Accumulate Householder reflectors
*
.AND..GT.         IF( WANTU1  P  0 ) THEN
            CALL ZLACPY( 'l', P, Q, X11, LDX11, U1, LDU1 )
            CALL ZUNGQR( P, P, Q, U1, LDU1, WORK(ITAUP1), WORK(IORGQR),
     $                   LORGQR, CHILDINFO )
         END IF
.AND..GT.         IF( WANTU2  M-P  0 ) THEN
            CALL ZLACPY( 'l', m-p, q, x21, ldx21, u2, ldu2 )
            CALL zungqr( m-p, m-p, q, u2, ldu2, work(itaup2),
     $                   work(iorgqr), lorgqr, childinfo )
         END IF
         IF( wantv1t .AND. q .GT. 0 ) THEN
            v1t(1,1) = one
            DO j = 2, q
               v1t(1,j) = zero
               v1t(j,1) = zero
            END DO
            CALL zlacpy( 'U', q-1, q-1, x21(1,2), ldx21, v1t(2,2),
     $                   ldv1t )
            CALL zunglq( q-1, q-1, q-1, v1t(2,2), ldv1t, work(itauq1),
     $                   work(iorglq), lorglq, childinfo )
         END IF
*
*        Simultaneously diagonalize X11 and X21.
*
         CALL zbbcsd( jobu1, jobu2, jobv1t, 'N', 'N', m, p, q, theta,
     $                rwork(iphi), u1, ldu1, u2, ldu2, v1t, ldv1t, cdum,
     $                1, rwork(ib11d), rwork(ib11e), rwork(ib12d),
     $                rwork(ib12e), rwork(ib21d), rwork(ib21e),
     $                rwork(ib22d), rwork(ib22e), rwork(ibbcsd),
     $                lrwork-ibbcsd+1, childinfo )
*
*        Permute rows and columns to place zero submatrices in
*        preferred positions
*
         IF( q .GT. 0 .AND. wantu2 ) THEN
            DO i = 1, q
               iwork(i) = m - p - q + i
            END DO
            DO i = q + 1, m - p
               iwork(i) = i - q
            END DO
            CALL zlapmt( .false., m-p, m-p, u2, ldu2, iwork )
         END IF
      ELSE IF( r .EQ. p ) THEN
*
*        Case 2: R = P
*
*        Simultaneously bidiagonalize X11 and X21
*
         CALL zunbdb2( m, p, q, x11, ldx11, x21, ldx21, theta,
     $                 rwork(iphi), work(itaup1), work(itaup2),
     $                 work(itauq1), work(iorbdb), lorbdb, childinfo )
*
*        Accumulate Householder reflectors
*
         IF( wantu1 .AND. p .GT. 0 ) THEN
            u1(1,1) = one
            DO j = 2, p
               u1(1,j) = zero
               u1(j,1) = zero
            END DO
            CALL zlacpy( 'L', p-1, p-1, x11(2,1), ldx11, u1(2,2), ldu1 )
            CALL zungqr( p-1, p-1, p-1, u1(2,2), ldu1, work(itaup1),
     $                   work(iorgqr), lorgqr, childinfo )
         END IF
         IF( wantu2 .AND. m-p .GT. 0 ) THEN
            CALL zlacpy( 'L', m-p, q, x21, ldx21, u2, ldu2 )
            CALL zungqr( m-p, m-p, q, u2, ldu2, work(itaup2),
     $                   work(iorgqr), lorgqr, childinfo )
         END IF
         IF( wantv1t .AND. q .GT. 0 ) THEN
            CALL zlacpy( 'U', p, q, x11, ldx11, v1t, ldv1t )
            CALL zunglq( q, q, r, v1t, ldv1t, work(itauq1),
     $                   work(iorglq), lorglq, childinfo )
         END IF
*
*        Simultaneously diagonalize X11 and X21.
*
         CALL zbbcsd( jobv1t, 'N', jobu1, jobu2, 'T', m, q, p, theta,
     $                rwork(iphi), v1t, ldv1t, cdum, 1, u1, ldu1, u2,
     $                ldu2, rwork(ib11d), rwork(ib11e), rwork(ib12d),
     $                rwork(ib12e), rwork(ib21d), rwork(ib21e),
     $                rwork(ib22d), rwork(ib22e), rwork(ibbcsd), lbbcsd,
     $                childinfo )
*
*        Permute rows and columns to place identity submatrices in
*        preferred positions
*
         IF( q .GT. 0 .AND. wantu2 ) THEN
            DO i = 1, q
               iwork(i) = m - p - q + i
            END DO
            DO i = q + 1, m - p
               iwork(i) = i - q
            END DO
            CALL zlapmt( .false., m-p, m-p, u2, ldu2, iwork )
         END IF
      ELSE IF( r .EQ. m-p ) THEN
*
*        Case 3: R = M-P
*
*        Simultaneously bidiagonalize X11 and X21
*
         CALL zunbdb3( m, p, q, x11, ldx11, x21, ldx21, theta,
     $                 rwork(iphi), work(itaup1), work(itaup2),
     $                 work(itauq1), work(iorbdb), lorbdb, childinfo )
*
*        Accumulate Householder reflectors
*
         IF( wantu1 .AND. p .GT. 0 ) THEN
            CALL zlacpy( 'L', p, q, x11, ldx11, u1, ldu1 )
            CALL zungqr( p, p, q, u1, ldu1, work(itaup1), work(iorgqr),
     $                   lorgqr, childinfo )
         END IF
         IF( wantu2 .AND. m-p .GT. 0 ) THEN
            u2(1,1) = one
            DO j = 2, m-p
               u2(1,j) = zero
               u2(j,1) = zero
            END DO
            CALL zlacpy( 'L', m-p-1, m-p-1, x21(2,1), ldx21, u2(2,2),
     $                   ldu2 )
            CALL zungqr( m-p-1, m-p-1, m-p-1, u2(2,2), ldu2,
     $                   work(itaup2), work(iorgqr), lorgqr, childinfo )
         END IF
         IF( wantv1t .AND. q .GT. 0 ) THEN
            CALL zlacpy( 'U', m-p, q, x21, ldx21, v1t, ldv1t )
            CALL zunglq( q, q, r, v1t, ldv1t, work(itauq1),
     $                   work(iorglq), lorglq, childinfo )
         END IF
*
*        Simultaneously diagonalize X11 and X21.
*
         CALL zbbcsd( 'N', jobv1t, jobu2, jobu1, 'T', m, m-q, m-p,
     $                theta, rwork(iphi), cdum, 1, v1t, ldv1t, u2, ldu2,
     $                u1, ldu1, rwork(ib11d), rwork(ib11e),
     $                rwork(ib12d), rwork(ib12e), rwork(ib21d),
     $                rwork(ib21e), rwork(ib22d), rwork(ib22e),
     $                rwork(ibbcsd), lbbcsd, childinfo )
*
*        Permute rows and columns to place identity submatrices in
*        preferred positions
*
         IF( q .GT. r ) THEN
            DO i = 1, r
               iwork(i) = q - r + i
            END DO
            DO i = r + 1, q
               iwork(i) = i - r
            END DO
            IF( wantu1 ) THEN
               CALL zlapmt( .false., p, q, u1, ldu1, iwork )
            END IF
            IF( wantv1t ) THEN
               CALL zlapmr( .false., q, q, v1t, ldv1t, iwork )
            END IF
         END IF
      ELSE
*
*        Case 4: R = M-Q
*
*        Simultaneously bidiagonalize X11 and X21
*
         CALL zunbdb4( m, p, q, x11, ldx11, x21, ldx21, theta,
     $                 rwork(iphi), work(itaup1), work(itaup2),
     $                 work(itauq1), work(iorbdb), work(iorbdb+m),
     $                 lorbdb-m, childinfo )
*
*        Accumulate Householder reflectors
*
         IF( wantu2 .AND. m-p .GT. 0 ) THEN
            CALL zcopy( m-p, work(iorbdb+p), 1, u2, 1 )
         END IF
         IF( wantu1 .AND. p .GT. 0 ) THEN
            CALL zcopy( p, work(iorbdb), 1, u1, 1 )
            DO j = 2, p
               u1(1,j) = zero
            END DO
            CALL zlacpy( 'L', p-1, m-q-1, x11(2,1), ldx11, u1(2,2),
     $                   ldu1 )
            CALL zungqr( p, p, m-q, u1, ldu1, work(itaup1),
     $                   work(iorgqr), lorgqr, childinfo )
         END IF
         IF( wantu2 .AND. m-p .GT. 0 ) THEN
            DO j = 2, m-p
               u2(1,j) = zero
            END DO
            CALL zlacpy( 'L', m-p-1, m-q-1, x21(2,1), ldx21, u2(2,2),
     $                   ldu2 )
            CALL zungqr( m-p, m-p, m-q, u2, ldu2, work(itaup2),
     $                   work(iorgqr), lorgqr, childinfo )
         END IF
         IF( wantv1t .AND. q .GT. 0 ) THEN
            CALL zlacpy( 'U', m-q, q, x21, ldx21, v1t, ldv1t )
            CALL zlacpy( 'U', p-(m-q), q-(m-q), x11(m-q+1,m-q+1), ldx11,
     $                   v1t(m-q+1,m-q+1), ldv1t )
            CALL zlacpy( 'U', -p+q, q-p, x21(m-q+1,p+1), ldx21,
     $                   v1t(p+1,p+1), ldv1t )
            CALL zunglq( q, q, q, v1t, ldv1t, work(itauq1),
     $                   work(iorglq), lorglq, childinfo )
         END IF
*
*        Simultaneously diagonalize X11 and X21.
*
         CALL zbbcsd( jobu2, jobu1, 'N', jobv1t, 'N', m, m-p, m-q,
     $                theta, rwork(iphi), u2, ldu2, u1, ldu1, cdum, 1,
     $                v1t, ldv1t, rwork(ib11d), rwork(ib11e),
     $                rwork(ib12d), rwork(ib12e), rwork(ib21d),
     $                rwork(ib21e), rwork(ib22d), rwork(ib22e),
     $                rwork(ibbcsd), lbbcsd, childinfo )
*
*        Permute rows and columns to place identity submatrices in
*        preferred positions
*
         IF( p .GT. r ) THEN
            DO i = 1, r
               iwork(i) = p - r + i
            END DO
            DO i = r + 1, p
               iwork(i) = i - r
            END DO
            IF( wantu1 ) THEN
               CALL zlapmt( .false., p, p, u1, ldu1, iwork )
            END IF
            IF( wantv1t ) THEN
               CALL zlapmr( .false., p, q, v1t, ldv1t, iwork )
            END IF
         END IF
      END IF
*
      RETURN
*
*     End of ZUNCSD2BY1
*
      END