dlarz(3)

NAME

DLARZ - applie a real elementary reflector H to a real M

by-N matrix C, from either the left or the right

SYNOPSIS

SUBROUTINE  DLARZ(  SIDE,  M,  N, L, V, INCV, TAU, C, LDC,
WORK )
    CHARACTER     SIDE
    INTEGER       INCV, L, LDC, M, N
    DOUBLE        PRECISION TAU
    DOUBLE        PRECISION C( LDC, * ), V( * ), WORK( * )

PURPOSE

DLARZ applies a real elementary reflector H to a real M

by-N matrix C, from either the left or the right. H is represent

ed in the form

H = I - tau * v * v'

where tau is a real scalar and v is a real vector.

If tau = 0, then H is taken to be the unit matrix.

H is a product of k elementary reflectors as returned by

DTZRZF.

ARGUMENTS

SIDE (input) CHARACTER*1

= 'L': form H * C
= 'R': form C * H

M (input) INTEGER

The number of rows of the matrix C.

N (input) INTEGER

The number of columns of the matrix C.

L (input) INTEGER

The number of entries of the vector V containing

the meaningful part of the Householder vectors. If SIDE = 'L', M

>= L >= 0, if SIDE = 'R', N >= L >= 0.

V (input) DOUBLE PRECISION array, dimension

(1+(L-1)*abs(INCV))

The vector v in the representation of H as re

turned by DTZRZF. V is not used if TAU = 0.

INCV (input) INTEGER

The increment between elements of v. INCV <> 0.

TAU (input) DOUBLE PRECISION

The value tau in the representation of H.

C (input/output) DOUBLE PRECISION array, dimension

(LDC,N)

On entry, the M-by-N matrix C. On exit, C is

overwritten by the matrix H * C if SIDE = 'L', or C * H if SIDE =

'R'.

LDC (input) INTEGER

The leading dimension of the array C. LDC >=

max(1,M).

WORK (workspace) DOUBLE PRECISION array, dimension

(N) if SIDE = 'L' or (M) if SIDE = 'R'

FURTHER DETAILS

Based on contributions by

A. Petitet, Computer Science Dept., Univ. of Tenn.,

Knoxville, USA

LAPACK version 3.0 15 June 2000

DLARZ(3)