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# dorm2r

```
NAME
DORM2R - 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 DORM2R( 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
DORM2R overwrites the general real m by n matrix C with

where Q is a real orthogonal matrix defined as the product
of k elementary reflectors

Q = H(1) H(2) . . . H(k)

as returned by DGEQRF. 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 elementary reflector H(i), for i =

1,2,...,k, as returned by DGEQRF in the first k
columns of its array argument A.  A is modified 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 elemen-
tary reflector H(i), as returned by DGEQRF.

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
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