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

# dlarfb(3lapack)

applies a real block reflector H or its transpose H' to a real m by n matrix C, from either the left or the right

## NAME

DLARFB - applies a real block reflector H or its transpose H' to a real m by n matrix C, from either the left or the right

## SYNOPSIS

- SUBROUTINE DLARFB(

  SIDE, TRANS, DIRECT, STOREV, M, N, K, V, LDV, T, LDT, C, LDC, WORK, LDWORK )

- IMPLICIT

  NONE

- CHARACTER

  DIRECT, SIDE, STOREV, TRANS

- INTEGER

  K, LDC, LDT, LDV, LDWORK, M, N

- DOUBLE

  PRECISION C( LDC, \* ), T( LDT, \* ), V( LDV, \* ), WORK( LDWORK, \* )

## PURPOSE

DLARFB applies a real block reflector H or its transpose H' to a real m by n matrix C, from either the left or the right.

## ARGUMENTS

- SIDE (input) CHARACTER\*1

  \= 'L': apply H or H' from the Left\
   \= 'R': apply H or H' from the Right

- TRANS (input) CHARACTER\*1

  \= 'N': apply H (No transpose)\
   \= 'T': apply H' (Transpose)

- DIRECT (input) CHARACTER\*1

  Indicates how H is formed from a product of elementary reflectors = 'F': H = H(1) H(2) . . . H(k) (Forward)\
   \= 'B': H = H(k) . . . H(2) H(1) (Backward)

- STOREV (input) CHARACTER\*1

  Indicates how the vectors which define the elementary reflectors are stored:\
   \= 'C': Columnwise\
   \= 'R': Rowwise

- M (input) INTEGER

  The number of rows of the matrix C.

- N (input) INTEGER

  The number of columns of the matrix C.

- K (input) INTEGER

  The order of the matrix T (= the number of elementary reflectors whose product defines the block reflector).

- V (input) DOUBLE PRECISION array, dimension

  (LDV,K) if STOREV = 'C' (LDV,M) if STOREV = 'R' and SIDE = 'L' (LDV,N) if STOREV = 'R' and SIDE = 'R' The matrix V. See further details.

- LDV (input) INTEGER

  The leading dimension of the array V. If STOREV = 'C' and SIDE = 'L', LDV \>= max(1,M); if STOREV = 'C' and SIDE = 'R', LDV \>= max(1,N); if STOREV = 'R', LDV \>= K.

- T (input) DOUBLE PRECISION array, dimension (LDT,K)

  The triangular k by k matrix T in the representation of the block reflector.

- LDT (input) INTEGER

  The leading dimension of the array T. LDT \>= K.

- C (input/output) DOUBLE PRECISION array, dimension (LDC,N)

  On entry, the m by n matrix C. On exit, C is overwritten by H\*C or H'\*C or C\*H or C\*H'.

- LDC (input) INTEGER

  The leading dimension of the array C. LDA \>= max(1,M).

- WORK (workspace) DOUBLE PRECISION array, dimension (LDWORK,K)

  - LDWORK (input) INTEGER

  The leading dimension of the array WORK. If SIDE = 'L', LDWORK \>= max(1,N); if SIDE = 'R', LDWORK \>= max(1,M).