To avoid division by zero!
function x = normalize(x, eps)
% Normalize vector `x` (zero mean, unit variance)
% default values
if (~exist('eps', 'var'))
eps = 1e-6;
end
mu = mean(x(:));
sigma = std(x(:));
if sigma < eps
sigma = 1;
end
x = (x - mu) / sigma;
end