function e = entropy(x, y)%ENTROPY Computes entropy e for vector x or joint entropy for (x, y).%%   e = entropy(x)%   e = entropy(x, y)%% Computes entropy e for vector x or joint entropy for (x, y). This% function uses base number 1024 for the logarithm.%%% This file is part of the Matlab Toolbox for Dimensionality Reduction v0.3b.% The toolbox can be obtained from http://www.cs.unimaas.nl/l.vandermaaten% You are free to use, change, or redistribute this code in any way you% want for non-commercial purposes. However, it is appreciated if you % maintain the name of the original author.%% (C) Laurens van der Maaten% Maastricht University, 2007    warning off        % Compute relative frequency of values    x = x(1:end);    if nargin == 1                p = freq(double(x));    else        if numel(x) ~= numel(y)            e = -1;            warning('Sizes of vector do not match.');            return;        end        y = y(1:end);        p = joint_freq(double(x), double(y));    end    % Compute Shannon entropy    xlogy(repmat(256, [length(p) 1]), p);    e = -sum(p .* xlogy(repmat(256, [length(p) 1]), p));