dormql(3)

NAME

DORMQL - overwrite the general real M-by-N matrix C with

SIDE = 'L' SIDE = 'R' TRANS = 'N'

SYNOPSIS

SUBROUTINE  DORMQL(  SIDE, TRANS, M, N, K, A, LDA, TAU, C,
LDC, WORK, LWORK, INFO )
    CHARACTER      SIDE, TRANS
    INTEGER        INFO, K, LDA, LDC, LWORK, M, N
    DOUBLE         PRECISION A( LDA, * ),  C(  LDC,  *  ),
TAU( * ), WORK( * )

PURPOSE

DORMQL overwrites the general real M-by-N matrix C with

SIDE = 'L' SIDE = 'R' TRANS = 'N': Q * C C * Q TRANS = 'T':

Q**T * C C * Q**T

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**T from the Left;
= 'R': apply Q or Q**T from the Right.

TRANS (input) CHARACTER*1

= 'N': No transpose, apply Q;
= 'T': Transpose, apply Q**T.

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 de

fines the elementary reflector H(i), for i = 1,2,...,k, as re

turned 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 ele

mentary 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**T*C or C*Q**T or C*Q.

LDC (input) INTEGER

The leading dimension of the array C. LDC >=

max(1,M).

WORK (workspace/output) DOUBLE PRECISION array, dimen

sion (LWORK)

On exit, if INFO = 0, WORK(1) returns the optimal

LWORK.

LWORK (input) INTEGER

The dimension of the array WORK. If SIDE = 'L',

LWORK >= max(1,N); if SIDE = 'R', LWORK >= max(1,M). For optimum

performance LWORK >= N*NB if SIDE = 'L', and LWORK >= M*NB if

SIDE = 'R', where NB is the optimal blocksize.

If LWORK = -1, then a workspace query is assumed;

the routine only calculates the optimal size of the WORK array,

returns this value as the first entry of the WORK array, and no

error message related to LWORK is issued by XERBLA.

INFO (output) INTEGER

= 0: successful exit
< 0: if INFO = -i, the i-th argument had an ille

gal value

LAPACK version 3.0 15 June 2000

DORMQL(3)