Entropy: Returns entropy (in bits) of each column of 'X'
by Will Dwinnell
H = Entropy(X)
H = row vector of calculated entropies (in bits)
X = data to be analyzed
Note 1: Each distinct value in X is considered a unique value.
Note 2: Estimated entropy values are slightly less than true,
due to finite sample size.
X = ceil(repmat([2 4 8 16],[1e3,1]) .* rand(1e3,4));