Contents
dlarz - applies a real elementary reflector H to a real M-
by-N matrix C, from either the left or the right
SUBROUTINE DLARZ(SIDE, M, N, L, V, INCV, TAU, C, LDC, WORK)
CHARACTER * 1 SIDE
INTEGER M, N, L, INCV, LDC
DOUBLE PRECISION TAU
DOUBLE PRECISION V(*), C(LDC,*), WORK(*)
SUBROUTINE DLARZ_64(SIDE, M, N, L, V, INCV, TAU, C, LDC, WORK)
CHARACTER * 1 SIDE
INTEGER*8 M, N, L, INCV, LDC
DOUBLE PRECISION TAU
DOUBLE PRECISION V(*), C(LDC,*), WORK(*)
F95 INTERFACE
SUBROUTINE LARZ(SIDE, [M], [N], L, V, [INCV], TAU, C, [LDC], [WORK])
CHARACTER(LEN=1) :: SIDE
INTEGER :: M, N, L, INCV, LDC
REAL(8) :: TAU
REAL(8), DIMENSION(:) :: V, WORK
REAL(8), DIMENSION(:,:) :: C
SUBROUTINE LARZ_64(SIDE, [M], [N], L, V, [INCV], TAU, C, [LDC], [WORK])
CHARACTER(LEN=1) :: SIDE
INTEGER(8) :: M, N, L, INCV, LDC
REAL(8) :: TAU
REAL(8), DIMENSION(:) :: V, WORK
REAL(8), DIMENSION(:,:) :: C
C INTERFACE
#include <sunperf.h>
void dlarz(char side, int m, int n, int l, double *v, int
incv, double tau, double *c, int ldc);
void dlarz_64(char side, long m, long n, long l, double *v,
long incv, double tau, double *c, long ldc);
dlarz 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
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
STZRZF.
SIDE (input)
= 'L': form H * C
= 'R': form C * H
M (input) The number of rows of the matrix C.
N (input) The number of columns of the matrix C.
L (input) 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) The vector v in the representation of H as
returned by STZRZF. V is not used if TAU = 0.
INCV (input)
The increment between elements of v. INCV <> 0.
TAU (input)
The value tau in the representation of H.
C (input/output)
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)
The leading dimension of the array C. LDC >=
max(1,M).
WORK (workspace)
(N) if SIDE = 'L' or (M) if SIDE = 'R'
Based on contributions by
A. Petitet, Computer Science Dept., Univ. of Tenn., Knox-
ville, USA