DLARZB(3f)

NAME
DLARZB - a real block reflector H or its transpose H**T to a real distributed M-by-N C from the left or the right

SYNOPSIS

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

CHARACTER
    DIRECT, SIDE, STOREV, TRANS

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

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

PURPOSE
DLARZB applies a real block reflector H or its transpose H**T to a real distributed M-by-N C from the left or the right. Currently, only STOREV = 'R' and DIRECT = 'B' are supported.

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)
    = 'C': 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, not supported yet)
    = '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 (not supported yet)
    = '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).

L       (input) INTEGER
    The number of columns of the matrix V containing the meaningful part of the Householder reflectors. If SIDE = 'L', M >= L >= 0, if SIDE = 'R', N >= L >= 0.

V       (input) DOUBLE PRECISION array, dimension (LDV,NV).
    If STOREV = 'C', NV = K; if STOREV = 'R', NV = L.

LDV     (input) INTEGER
    The leading dimension of the array V. If STOREV = 'C', LDV >= L; 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. LDC >= 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).

FURTHER DETAILS
Based on contributions by
  A. Petitet, Computer Science Dept., Univ. of Tenn., Knoxville, USA