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zunbdb.f(3) LAPACK zunbdb.f(3)

zunbdb.f -


subroutine zunbdb (TRANS, SIGNS, M, P, Q, X11, LDX11, X12, LDX12, X21, LDX21, X22, LDX22, THETA, PHI, TAUP1, TAUP2, TAUQ1, TAUQ2, WORK, LWORK, INFO)
 
ZUNBDB

ZUNBDB
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.
Parameters:
TRANS
          TRANS is 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
          SIGNS is CHARACTER
          = 'O':      The lower-left block is made nonpositive (the
                      "other" convention);
          otherwise:  The upper-right block is made nonpositive (the
                      "default" convention).
M
          M is INTEGER
          The number of rows and columns in X.
P
          P is INTEGER
          The number of rows in X11 and X12. 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*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
          LDX11 is INTEGER
          The leading dimension of X11. If TRANS = 'N', then LDX11 >=
          P; else LDX11 >= Q.
X12
          X12 is 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
          LDX12 is INTEGER
          The leading dimension of X12. If TRANS = 'N', then LDX12 >=
          P; else LDX11 >= M-Q.
X21
          X21 is 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
          LDX21 is INTEGER
          The leading dimension of X21. If TRANS = 'N', then LDX21 >=
          M-P; else LDX21 >= Q.
X22
          X22 is 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
          LDX22 is INTEGER
          The leading dimension of X22. If TRANS = 'N', then LDX22 >=
          M-P; else LDX22 >= M-Q.
THETA
          THETA is 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
          PHI is 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
          TAUP1 is COMPLEX*16 array, dimension (P)
          The scalar factors of the elementary reflectors that define
          P1.
TAUP2
          TAUP2 is COMPLEX*16 array, dimension (M-P)
          The scalar factors of the elementary reflectors that define
          P2.
TAUQ1
          TAUQ1 is COMPLEX*16 array, dimension (Q)
          The scalar factors of the elementary reflectors that define
          Q1.
TAUQ2
          TAUQ2 is COMPLEX*16 array, dimension (M-Q)
          The scalar factors of the elementary reflectors that define
          Q2.
WORK
          WORK is COMPLEX*16 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.
Date:
November 2013
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.
References:
[1] Brian D. Sutton. Computing the complete CS decomposition. Numer. Algorithms, 50(1):33-65, 2009.
Definition at line 286 of file zunbdb.f.

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