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 where Q is a real orthogonal matrix defined as the product of k elementary 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 elementary reflector H(i), for i = 1,2,...,k, as returned by DGEQLF in the last 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 elementary reflector 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