LAPACK  3.4.2 LAPACK: Linear Algebra PACKage
dlarfg.f File Reference

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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).

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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:
 [in] N ``` N is INTEGER The order of the elementary reflector.``` [in,out] ALPHA ``` ALPHA is DOUBLE PRECISION On entry, the value alpha. On exit, it is overwritten with the value beta.``` [in,out] 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.``` [in] INCX ``` INCX is INTEGER The increment between elements of X. INCX > 0.``` [out] TAU ``` TAU is DOUBLE PRECISION The value tau.```
Date:
September 2012

Definition at line 107 of file dlarfg.f.

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