1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
|
function [v,beta,xnorm] = hmake1 (x)
%HMAKE1 construct a Householder reflection
% Example:
% [v,beta,xnorm] = hmake1 (x)
% See also: testall
% Copyright 2006-2007, Timothy A. Davis.
% http://www.cise.ufl.edu/research/sparse
n = length (x) ;
if (n == 1)
v = 1 ;
xnorm = norm (x) ;
if (x (1) < 0)
beta = 2 ;
else
beta = 0 ;
end
return
end
sigma = x (2:n)'*x(2:n) ;
xnorm = sqrt (x (1)^2 + sigma) ;
v = x ;
if (sigma == 0)
v (1) = 1 ;
if (x (1) < 0)
beta = 2 ;
else
beta = 0 ;
end
else
if (x (1) <= 0)
v (1) = x(1) - xnorm ;
else
v (1) = -sigma / (x(1) + xnorm) ;
end
beta = (2*v(1)^2) / (sigma + v(1)^2) ;
v = v / v(1) ;
end
|
