dlarfg-f(3)

dlarfg.f –

Synopsis

Functions/Subroutines

subroutine dlarfg (N, ALPHA, X, INCX, TAU)
DLARFG generates an elementary reflector (Householder matrix).

Function/Subroutine Documentation

subroutine dlarfg (integerN, double precisionALPHA, double precision, dimension( * )X, integerINCX, double precisionTAU)

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.

Date:

September 2012

Definition at line 107 of file dlarfg.f.

Author

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