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cungbr.f(3) LAPACK cungbr.f(3)

NAME

cungbr.f

SYNOPSIS

Functions/Subroutines


subroutine cungbr (VECT, M, N, K, A, LDA, TAU, WORK, LWORK, INFO)
CUNGBR

Function/Subroutine Documentation

subroutine cungbr (character VECT, integer M, integer N, integer K, complex, dimension( lda, * ) A, integer LDA, complex, dimension( * ) TAU, complex, dimension( * ) WORK, integer LWORK, integer INFO)

CUNGBR

Purpose:


CUNGBR generates one of the complex unitary matrices Q or P**H
determined by CGEBRD when reducing a complex matrix A to bidiagonal
form: A = Q * B * P**H. Q and P**H are defined as products of
elementary reflectors H(i) or G(i) respectively.
If VECT = 'Q', A is assumed to have been an M-by-K matrix, and Q
is of order M:
if m >= k, Q = H(1) H(2) . . . H(k) and CUNGBR returns the first n
columns of Q, where m >= n >= k;
if m < k, Q = H(1) H(2) . . . H(m-1) and CUNGBR returns Q as an
M-by-M matrix.
If VECT = 'P', A is assumed to have been a K-by-N matrix, and P**H
is of order N:
if k < n, P**H = G(k) . . . G(2) G(1) and CUNGBR returns the first m
rows of P**H, where n >= m >= k;
if k >= n, P**H = G(n-1) . . . G(2) G(1) and CUNGBR returns P**H as
an N-by-N matrix.

Parameters:

VECT


VECT is CHARACTER*1
Specifies whether the matrix Q or the matrix P**H is
required, as defined in the transformation applied by CGEBRD:
= 'Q': generate Q;
= 'P': generate P**H.

M


M is INTEGER
The number of rows of the matrix Q or P**H to be returned.
M >= 0.

N


N is INTEGER
The number of columns of the matrix Q or P**H to be returned.
N >= 0.
If VECT = 'Q', M >= N >= min(M,K);
if VECT = 'P', N >= M >= min(N,K).

K


K is INTEGER
If VECT = 'Q', the number of columns in the original M-by-K
matrix reduced by CGEBRD.
If VECT = 'P', the number of rows in the original K-by-N
matrix reduced by CGEBRD.
K >= 0.

A


A is COMPLEX array, dimension (LDA,N)
On entry, the vectors which define the elementary reflectors,
as returned by CGEBRD.
On exit, the M-by-N matrix Q or P**H.

LDA


LDA is INTEGER
The leading dimension of the array A. LDA >= M.

TAU


TAU is COMPLEX array, dimension
(min(M,K)) if VECT = 'Q'
(min(N,K)) if VECT = 'P'
TAU(i) must contain the scalar factor of the elementary
reflector H(i) or G(i), which determines Q or P**H, as
returned by CGEBRD in its array argument TAUQ or TAUP.

WORK


WORK is COMPLEX array, dimension (MAX(1,LWORK))
On exit, if INFO = 0, WORK(1) returns the optimal LWORK.

LWORK


LWORK is INTEGER
The dimension of the array WORK. LWORK >= max(1,min(M,N)).
For optimum performance LWORK >= min(M,N)*NB, where NB
is the optimal blocksize.
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:

April 2012

Definition at line 159 of file cungbr.f.

Author

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Tue Nov 14 2017 Version 3.8.0