SRC/cunbdb1.f(3)

NAME
SRC/cunbdb1.f

SYNOPSIS

  Functions/Subroutines
subroutine cunbdb1 (m, p, q, x11, ldx11, x21, ldx21, theta, phi, taup1, taup2, tauq1, work, lwork, info)
CUNBDB1

Function/Subroutine Documentation

  subroutine cunbdb1 (integer m, integer p, integer q, complex, dimension(ldx11,*) x11, integer ldx11, complex, dimension(ldx21,*) x21, integer ldx21, real, dimension(*) theta, real, dimension(*) phi, complex, dimension(*) taup1, complex, dimension(*) taup2, complex, dimension(*) tauq1, complex, dimension(*) work, integer lwork, integer info)

CUNBDB1

Purpose:

     CUNBDB1 simultaneously bidiagonalizes the blocks of a tall and skinny
     matrix X with orthonormal columns:
                                [ B11 ]
          [ X11 ]   [ P1 |    ] [  0  ]
          [-----] = [---------] [-----] Q1**T .
          [ X21 ]   [    | P2 ] [ B21 ]
                                [  0  ]
     X11 is P-by-Q, and X21 is (M-P)-by-Q. Q must be no larger than P,
     M-P, or M-Q. Routines CUNBDB2, CUNBDB3, and CUNBDB4 handle cases in
     which Q is not the minimum dimension.
     The unitary matrices P1, P2, and Q1 are P-by-P, (M-P)-by-(M-P),
     and (M-Q)-by-(M-Q), respectively. They are represented implicitly by
     Householder vectors.
     B11 and B12 are Q-by-Q bidiagonal matrices represented implicitly by
     angles THETA, PHI.

Parameters
    M

              M is INTEGER
               The number of rows X11 plus the number of rows in X21.

    P

              P is INTEGER
               The number of rows in X11. 0 <= P <= M.

    Q

              Q is INTEGER
               The number of columns in X11 and X21. 0 <= Q <=
               MIN(P,M-P,M-Q).

    X11

              X11 is COMPLEX array, dimension (LDX11,Q)
               On entry, the top block of the matrix X to be reduced. On
               exit, the columns of tril(X11) specify reflectors for P1 and
               the rows of triu(X11,1) specify reflectors for Q1.

    LDX11

              LDX11 is INTEGER
               The leading dimension of X11. LDX11 >= P.

    X21

              X21 is COMPLEX array, dimension (LDX21,Q)
               On entry, the bottom block of the matrix X to be reduced. On
               exit, the columns of tril(X21) specify reflectors for P2.

    LDX21

              LDX21 is INTEGER
               The leading dimension of X21. LDX21 >= M-P.

    THETA

              THETA is REAL array, dimension (Q)
               The entries of the bidiagonal blocks B11, B21 are defined by
               THETA and PHI. See Further Details.

    PHI

              PHI is REAL array, dimension (Q-1)
               The entries of the bidiagonal blocks B11, B21 are defined by
               THETA and PHI. See Further Details.

    TAUP1

              TAUP1 is COMPLEX array, dimension (P)
               The scalar factors of the elementary reflectors that define
               P1.

    TAUP2

              TAUP2 is COMPLEX array, dimension (M-P)
               The scalar factors of the elementary reflectors that define
               P2.

    TAUQ1

              TAUQ1 is COMPLEX array, dimension (Q)
               The scalar factors of the elementary reflectors that define
               Q1.

    WORK

              WORK is COMPLEX array, dimension (LWORK)

    LWORK

              LWORK is 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

              INFO is INTEGER
               = 0:  successful exit.
               < 0:  if INFO = -i, the i-th argument had an illegal value.

Author
    Univ. of Tennessee

    Univ. of California Berkeley

    Univ. of Colorado Denver

    NAG Ltd.

Further Details:

      The upper-bidiagonal blocks B11, B21 are represented implicitly by
      angles THETA(1), ..., THETA(Q) and PHI(1), ..., PHI(Q-1). 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 CUNCSD for details.
      P1, P2, and Q1 are represented as products of elementary reflectors.
      See CUNCSD2BY1 for details on generating P1, P2, and Q1 using CUNGQR
      and CUNGLQ.

References:
    [1] Brian D. Sutton. Computing the complete CS decomposition. Numer. Algorithms, 50(1):33-65, 2009.

Definition at line 200 of file cunbdb1.f.

Author

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