dlarz (3)

Functions/Subroutines

subroutine dlarz (SIDE, M, N, L, V, INCV, TAU, C, LDC, WORK)

DLARZ applies an elementary reflector (as returned by stzrzf) to a general matrix.

subroutine dlarz (characterSIDE, integerM, integerN, integerL, double precision, dimension( * )V, integerINCV, double precisionTAU, double precision, dimension( ldc, * )C, integerLDC, double precision, dimension( * )WORK)

DLARZ applies an elementary reflector (as returned by stzrzf) to a general matrix.

Purpose:

 DLARZ 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**T

 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.

Parameters:

SIDE

          SIDE is CHARACTER*1
          = 'L': form  H * C
          = 'R': form  C * H

M

          M is INTEGER
          The number of rows of the matrix C.

N

          N is INTEGER
          The number of columns of the matrix C.

L

          L is 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

          V is 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

          INCV is INTEGER
          The increment between elements of v. INCV <> 0.

TAU

          TAU is DOUBLE PRECISION
          The value tau in the representation of H.

C

          C is 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

          LDC is INTEGER
          The leading dimension of the array C. LDC >= max(1,M).

WORK

          WORK is DOUBLE PRECISION array, dimension
                         (N) if SIDE = 'L'
                      or (M) if SIDE = 'R'

Author:

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Date:

September 2012

Contributors:

A. Petitet, Computer Science Dept., Univ. of Tenn., Knoxville, USA

Further Details:

Definition at line 146 of file dlarz.f.

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