LAPACK  3.4.1
LAPACK: Linear Algebra PACKage
dlarfg.f File Reference

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Functions/Subroutines

subroutine DLARFG (N, ALPHA, X, INCX, TAU)
 DLARFG

Function/Subroutine Documentation

subroutine DLARFG ( INTEGER  N,
DOUBLE PRECISION  ALPHA,
DOUBLE PRECISION, dimension( * )  X,
INTEGER  INCX,
DOUBLE PRECISION  TAU 
)

DLARFG

Download DLARFG + dependencies [TGZ] [ZIP] [TXT]
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.
 
Author:
Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.
Date:
November 2011

Definition at line 107 of file dlarfg.f.

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