NAME¶

DOPMTR - overwrites the general real M-by-N matrix C with SIDE = 'L' SIDE = 'R' TRANS = 'N'

SYNOPSIS¶

SUBROUTINE DOPMTR(

SIDE, UPLO, TRANS, M, N, AP, TAU, C, LDC, WORK, INFO )

CHARACTER SIDE, TRANS, UPLO INTEGER INFO, LDC, M, N DOUBLE PRECISION AP( * ), C( LDC, * ), TAU( * ), WORK( * )

PURPOSE¶

DOPMTR overwrites the general real M-by-N matrix C with TRANS = 'T': Q**T * C C * Q**T
where Q is a real orthogonal matrix of order nq, with nq = m if SIDE = 'L' and nq = n if SIDE = 'R'. Q is defined as the product of nq-1 elementary reflectors, as returned by DSPTRD using packed storage:
if UPLO = 'U', Q = H(nq-1) . . . H(2) H(1);
if UPLO = 'L', Q = H(1) H(2) . . . H(nq-1).

ARGUMENTS¶

SIDE (input) CHARACTER*1

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

UPLO (input) CHARACTER*1

= 'U': Upper triangular packed storage used in previous call to DSPTRD; = 'L': Lower triangular packed storage used in previous call to DSPTRD.

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.

AP (input) DOUBLE PRECISION array, dimension

(M*(M+1)/2) if SIDE = 'L' (N*(N+1)/2) if SIDE = 'R' The vectors which define the elementary reflectors, as returned by DSPTRD. AP is modified by the routine but restored on exit.

TAU (input) DOUBLE PRECISION array, dimension (M-1) if SIDE = 'L'

or (N-1) if SIDE = 'R' TAU(i) must contain the scalar factor of the elementary reflector H(i), as returned by DSPTRD.

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) 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