# dlarf (l) - Linux Man Pages

## NAME

DLARF - applies a real elementary reflector H to a real m by n matrix C, from either the left or the right

## SYNOPSIS

SUBROUTINE DLARF(
SIDE, M, N, V, INCV, TAU, C, LDC, WORK )

IMPLICIT NONE

CHARACTER SIDE

INTEGER INCV, LDC, M, N

DOUBLE PRECISION TAU

DOUBLE PRECISION C( LDC, * ), V( * ), WORK( * )

## PURPOSE

DLARF applies a real elementary reflector H to a real m by n matrix C, from either the left or the right. H is represented in the form
I - tau vaq
where tau is a real scalar and v is a real vector.
If tau = 0, then H is taken to be the unit matrix.

## ARGUMENTS

SIDE (input) CHARACTER*1
= aqLaq: form H * C
= aqRaq: 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.
V (input) DOUBLE PRECISION array, dimension
(1 + (M-1)*abs(INCV)) if SIDE = aqLaq or (1 + (N-1)*abs(INCV)) if SIDE = aqRaq The vector v in the representation of H. 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 = aqLaq, or C * H if SIDE = aqRaq.
LDC (input) INTEGER
The leading dimension of the array C. LDC >= max(1,M).
WORK (workspace) DOUBLE PRECISION array, dimension
(N) if SIDE = aqLaq or (M) if SIDE = aqRaq