SRC/dlarfg.f(3)

NAME
SRC/dlarfg.f

SYNOPSIS

  Functions/Subroutines
subroutine dlarfg (n, alpha, x, incx, tau)
DLARFG generates an elementary reflector (Householder matrix).

Function/Subroutine Documentation

  subroutine dlarfg (integer n, double precision alpha, double precision, dimension( * ) x, integer incx, double precision tau)

DLARFG generates an elementary reflector (Householder matrix).

Purpose:

    !>
    !> DLARFG generates a real elementary reflector H of order n, such
    !> that
    !>
    !>       H * ( alpha ) = ( beta ),   H**T * H = I.
    !>           (   x   )   (   0  )
    !>
    !> where alpha and beta are scalars, and x is an (n-1)-element real
    !> vector. H is represented in the form
    !>
    !>       H = I - tau * ( 1 ) * ( 1 v**T ) ,
    !>                     ( v )
    !>
    !> where tau is a real scalar and v is a real (n-1)-element
    !> vector.
    !>
    !> If the elements of x are all zero, then tau = 0 and H is taken to be
    !> the unit matrix.
    !>
    !> Otherwise  1 <= tau <= 2.
    !>

Parameters
    N

    !>          N is INTEGER
    !>          The order of the elementary reflector.
    !>

    ALPHA

    !>          ALPHA is DOUBLE PRECISION
    !>          On entry, the value alpha.
    !>          On exit, it is overwritten with the value beta.
    !>

    X

    !>          X is DOUBLE PRECISION array, dimension
    !>                         (1+(N-2)*abs(INCX))
    !>          On entry, the vector x.
    !>          On exit, it is overwritten with the vector v.
    !>

    INCX

    !>          INCX is INTEGER
    !>          The increment between elements of X. INCX > 0.
    !>

    TAU

    !>          TAU is DOUBLE PRECISION
    !>          The value tau.
    !>

Author
    Univ. of Tennessee

    Univ. of California Berkeley

    Univ. of Colorado Denver

    NAG Ltd.

Definition at line 105 of file dlarfg.f.

Author

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