dorgqr(3)

NAME

DORGQR - generate an M-by-N real matrix Q with orthonormal

columns,

SYNOPSIS

SUBROUTINE DORGQR( M, N, K, A, LDA, TAU, WORK, LWORK, INFO
)
    INTEGER        INFO, K, LDA, LWORK, M, N
    DOUBLE         PRECISION A( LDA, * ), TAU( * ),  WORK(
* )

PURPOSE

DORGQR generates an M-by-N real matrix Q with orthonormal

columns, which is defined as the first N columns of a product of

K elementary reflectors of order M

Q = H(1) H(2) . . . H(k)

as returned by DGEQRF.

ARGUMENTS

M (input) INTEGER

The number of rows of the matrix Q. M >= 0.

N (input) INTEGER

The number of columns of the matrix Q. M >= N >=

0.

K (input) INTEGER

The number of elementary reflectors whose product

defines the matrix Q. N >= K >= 0.

A (input/output) DOUBLE PRECISION array, dimension

(LDA,N)

On entry, the i-th column must contain the vector

which defines the elementary reflector H(i), for i = 1,2,...,k,

as returned by DGEQRF in the first k columns of its array argu

ment A. On exit, the M-by-N matrix Q.

LDA (input) INTEGER

The first dimension of the array A. LDA >=

max(1,M).

TAU (input) DOUBLE PRECISION array, dimension (K)

TAU(i) must contain the scalar factor of the ele

mentary reflector H(i), as returned by DGEQRF.

WORK (workspace/output) DOUBLE PRECISION array, dimen

sion (LWORK)

On exit, if INFO = 0, WORK(1) returns the optimal

LWORK.

LWORK (input) INTEGER

The dimension of the array WORK. LWORK >=

max(1,N). For optimum performance LWORK >= 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 (output) INTEGER

= 0: successful exit
< 0: if INFO = -i, the i-th argument has an ille

gal value

LAPACK version 3.0 15 June 2000

DORGQR(3)