# slarfb (l) - Linux Man Pages

## NAME

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

## SYNOPSIS

SUBROUTINE SLARFB(
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

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

## PURPOSE

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

## ARGUMENTS

SIDE (input) CHARACTER*1
= aqLaq: apply H or Haq from the Left
= aqRaq: apply H or Haq from the Right
TRANS (input) CHARACTER*1

= aqNaq: apply H (No transpose)
= aqTaq: apply Haq (Transpose)
DIRECT (input) CHARACTER*1
Indicates how H is formed from a product of elementary reflectors = aqFaq: H = H(1) H(2) . . . H(k) (Forward)
= aqBaq: H = H(k) . . . H(2) H(1) (Backward)
STOREV (input) CHARACTER*1
Indicates how the vectors which define the elementary reflectors are stored:
= aqCaq: Columnwise
= aqRaq: 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) REAL array, dimension
(LDV,K) if STOREV = aqCaq (LDV,M) if STOREV = aqRaq and SIDE = aqLaq (LDV,N) if STOREV = aqRaq and SIDE = aqRaq The matrix V. See further details.
LDV (input) INTEGER
The leading dimension of the array V. If STOREV = aqCaq and SIDE = aqLaq, LDV >= max(1,M); if STOREV = aqCaq and SIDE = aqRaq, LDV >= max(1,N); if STOREV = aqRaq, LDV >= K.
T (input) REAL 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) REAL array, dimension (LDC,N)
On entry, the m by n matrix C. On exit, C is overwritten by H*C or Haq*C or C*H or C*Haq.
LDC (input) INTEGER
The leading dimension of the array C. LDA >= max(1,M).
WORK (workspace) REAL array, dimension (LDWORK,K)
LDWORK (input) INTEGER
The leading dimension of the array WORK. If SIDE = aqLaq, LDWORK >= max(1,N); if SIDE = aqRaq, LDWORK >= max(1,M).