function u = house(x)
%
% compute householder transformation
% this is a stable version.
% 
% written by Ming Gu for Math 221, Fall 2008
%
x  = x(:);
n  = length(x);
if (norm(x) == 0)
    u = ones(n,1)/sqrt(n);
    return;
end
x(1) = x(1) +sign(x(1))*norm(x);
u    = x/norm(x);