1function [v,beta,xnorm] = hmake1 (x)
2%HMAKE1 construct a Householder reflection
3% Example:
4%   [v,beta,xnorm] = hmake1 (x)
5% See also: testall
6
7% Copyright 2006-2012, Timothy A. Davis, http://www.suitesparse.com
8
9n = length (x) ;
10if (n == 1)
11    v = 1 ;
12    xnorm = norm (x) ;
13    if (x (1) < 0)
14        beta = 2 ;
15    else
16        beta = 0 ;
17    end
18    return
19end
20sigma = x (2:n)'*x(2:n) ;
21xnorm = sqrt (x (1)^2 + sigma) ;
22v = x ;
23if (sigma == 0)
24    v (1) = 1 ;
25    if (x (1) < 0)
26        beta = 2 ;
27    else
28        beta = 0 ;
29    end
30else
31    if (x (1) <= 0)
32        v (1) = x(1) - xnorm ;
33    else
34        v (1) = -sigma / (x(1) + xnorm) ;
35    end
36    beta = (2*v(1)^2) / (sigma + v(1)^2) ;
37    v = v / v(1) ;
38end
39