DORM2L(l) ) DORM2L(l)NAME
DORM2L - overwrite the general real m by n matrix C with Q * C if SIDE
= 'L' and TRANS = 'N', or Q'* C if SIDE = 'L' and TRANS = 'T', or C *
Q if SIDE = 'R' and TRANS = 'N', or C * Q' if SIDE = 'R' and TRANS =
'T',
SYNOPSIS
SUBROUTINE DORM2L( SIDE, TRANS, M, N, K, A, LDA, TAU, C, LDC, WORK,
INFO )
CHARACTER SIDE, TRANS
INTEGER INFO, K, LDA, LDC, M, N
DOUBLE PRECISION A( LDA, * ), C( LDC, * ), TAU( * ), WORK(
* )
PURPOSE
DORM2L overwrites the general real m by n matrix C with Q * C if SIDE =
'L' and TRANS = 'N', or Q'* C if SIDE = 'L' and TRANS = 'T', or C * Q
if SIDE = 'R' and TRANS = 'N', or C * Q' if SIDE = 'R' and TRANS = 'T',
where Q is a real orthogonal matrix defined as the product of k elemen‐
tary reflectors
Q = H(k) . . . H(2)H(1)
as returned by DGEQLF. Q is of order m if SIDE = 'L' and of order n if
SIDE = 'R'.
ARGUMENTS
SIDE (input) CHARACTER*1
= 'L': apply Q or Q' from the Left
= 'R': apply Q or Q' from the Right
TRANS (input) CHARACTER*1
= 'N': apply Q (No transpose)
= 'T': apply Q' (Transpose)
M (input) INTEGER
The number of rows of the matrix C. M >= 0.
N (input) INTEGER
The number of columns of the matrix C. N >= 0.
K (input) INTEGER
The number of elementary reflectors whose product defines the
matrix Q. If SIDE = 'L', M >= K >= 0; if SIDE = 'R', N >= K >=
0.
A (input) DOUBLE PRECISION array, dimension (LDA,K)
The i-th column must contain the vector which defines the ele‐
mentary reflector H(i), for i = 1,2,...,k, as returned by DGE‐
QLF in the last k columns of its array argument A. A is modi‐
fied by the routine but restored on exit.
LDA (input) INTEGER
The leading dimension of the array A. If SIDE = 'L', LDA >=
max(1,M); if SIDE = 'R', LDA >= max(1,N).
TAU (input) DOUBLE PRECISION array, dimension (K)
TAU(i) must contain the scalar factor of the elementary reflec‐
tor H(i), as returned by DGEQLF.
C (input/output) DOUBLE PRECISION array, dimension (LDC,N)
On entry, the m by n matrix C. On exit, C is overwritten by
Q*C or Q'*C or C*Q' or C*Q.
LDC (input) INTEGER
The leading dimension of the array C. LDC >= max(1,M).
WORK (workspace) DOUBLE PRECISION array, dimension
(N) if SIDE = 'L', (M) if SIDE = 'R'
INFO (output) INTEGER
= 0: successful exit
< 0: if INFO = -i, the i-th argument had an illegal value
LAPACK version 3.0 15 June 2000 DORM2L(l)
