NAME

dlatzm - apply a Householder matrix generated by DTZRQF to a matrix

SYNOPSIS

SUBROUTINE DLATZM( SIDE, M, N, V, INCV, TAU, C1, C2, LDC, WORK )

CHARACTER SIDE

INTEGER INCV, LDC, M, N

DOUBLE PRECISION TAU

DOUBLE PRECISION C1( LDC, ∗ ), C2( LDC, ∗ ), V( ∗ ), WORK( ∗ )

#include <sunperf.h>

void dlatzm(char side, int m, int n, double ∗v, int incv, double tau, double ∗c1, double ∗c2, int ldc) ;

PURPOSE

DLATZM applies a Householder matrix generated by DTZRQF to a matrix. 
 
Let P = I - tau∗u∗u’,   u = ( 1 ),
                            ( v )
where v is an (m-1) vector if SIDE = ’L’, or a (n-1) vector if SIDE = ’R’.
 
If SIDE equals ’L’, let
       C = [ C1 ] 1
           [ C2 ] m-1
             n
Then C is overwritten by P∗C.
 
If SIDE equals ’R’, let
       C = [ C1, C2 ] m
              1  n-1
Then C is overwritten by C∗P.
 

ARGUMENTS

SIDE (input) CHARACTER∗1
= ’L’: form P ∗ C
= ’R’: form C ∗ P

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 = ’L’ (1 + (N-1)∗abs(INCV)) if SIDE = ’R’ The vector v in the representation of P. 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 P.

C1 (input/output) DOUBLE PRECISION array, dimension
(LDC,N) if SIDE = ’L’ (M,1)   if SIDE = ’R’ On entry, the n-vector C1 if SIDE = ’L’, or the m-vector C1 if SIDE = ’R’.
 
On exit, the first row of P∗C if SIDE = ’L’, or the first column of C∗P if SIDE = ’R’.

C2 (input/output) DOUBLE PRECISION array, dimension
(LDC, N)   if SIDE = ’L’ (LDC, N-1) if SIDE = ’R’ On entry, the (m - 1) x n matrix C2 if SIDE = ’L’, or the m x (n - 1) matrix C2 if SIDE = ’R’.
 
On exit, rows 2:m of P∗C if SIDE = ’L’, or columns 2:m of C∗P if SIDE = ’R’.

LDC (input) INTEGER
The leading dimension of the arrays C1 and C2. LDC >= (1,M).

WORK (workspace) DOUBLE PRECISION array, dimension
(N) if SIDE = ’L’ (M) if SIDE = ’R’

SunOS 5.0  —  Last change: 10 Dec 1998