---
name: "slarz"
section: "3lapack"
platform: "linux"
package: "liblapack-doc"
version: "3.2.1-8"
release: "Debian 6.0 (Squeeze)"
platforms: ["linux"]
url: "https://new.carta.tech/slarz/3lapack"
---

# slarz(3lapack)

applies a real elementary reflector H to a real M-by-N matrix C, from either the left or the right

## NAME

SLARZ - applies a real elementary reflector H to a real M-by-N matrix C, from either the left or the right

## SYNOPSIS

- SUBROUTINE SLARZ(

  SIDE, M, N, L, V, INCV, TAU, C, LDC, WORK )

- CHARACTER

  SIDE

- INTEGER

  INCV, L, LDC, M, N

- REAL

  TAU

- REAL

  C( LDC, \* ), V( \* ), WORK( \* )

## PURPOSE

SLARZ 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.

## 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) REAL array, dimension (1+(L-1)\*abs(INCV))

  The vector v in the representation of H as returned by STZRZF. V is not used if TAU = 0.

- INCV (input) INTEGER

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

- TAU (input) REAL

  The value tau in the representation of H.

- C (input/output) REAL 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) REAL 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