- SUBROUTINE DLARZ(
- SIDE, M, N, L, V, INCV, TAU, C, LDC, WORK )
- CHARACTER SIDE
- INTEGER INCV, L, LDC, M, N
- DOUBLE PRECISION TAU
- DOUBLE PRECISION C( LDC, * ), V( * ), WORK( * )
PURPOSEDLARZ applies a real elementary reflector H to a real M-by-N matrix C, from either the left or the right. H is represented in the form
H = I - tau * v * v'
where tau is a real scalar and v is a real vector.
If tau = 0, then H is taken to be the unit matrix.
H is a product of k elementary reflectors as returned by DTZRZF.
- SIDE (input) CHARACTER*1
= 'L': form H * C
= 'R': form C * H
- M (input) INTEGER
- The number of rows of the matrix C.
- N (input) INTEGER
- The number of columns of the matrix C.
- L (input) INTEGER
- The number of entries of the vector V containing the meaningful part of the Householder vectors. If SIDE = 'L', M >= L >= 0, if SIDE = 'R', N >= L >= 0.
- V (input) DOUBLE PRECISION array, dimension (1+(L-1)*abs(INCV))
- The vector v in the representation of H as returned by DTZRZF. V is not used if TAU = 0.
- INCV (input) INTEGER
- The increment between elements of v. INCV <> 0.
- TAU (input) DOUBLE PRECISION
- The value tau in the representation of H.
- C (input/output) DOUBLE PRECISION array, dimension (LDC,N)
- On entry, the M-by-N matrix C. On exit, C is overwritten by the matrix H * C if SIDE = 'L', or C * H if SIDE = 'R'.
- LDC (input) INTEGER
- The leading dimension of the array C. LDC >= max(1,M).
- WORK (workspace) DOUBLE PRECISION array, dimension
- (N) if SIDE = 'L' or (M) if SIDE = 'R'
FURTHER DETAILSBased on contributions by
A. Petitet, Computer Science Dept., Univ. of Tenn., Knoxville, USA