function [xpca xzca] = PCAwhite(x)
size(x)
x = x';
k= 10;
epsilon=1e-6;
avg = mean(x, 1)

x = x - repmat(avg, size(x, 1), 1);

sigma = x * x' / size(x, 2);
size(sigma)
[U,S,V] = svd(sigma);
%xRot = U' * x;          % rotated version of the data. 
%xTilde = U(:,1:k)' * x; % reduced dimension representation of the data, 
                         % where k is the number of eigenvectors to keep

xpca = diag(1./sqrt(diag(S) + epsilon)) * U' * x;
xzca = U * diag(1./sqrt(diag(S) + epsilon)) * U' * x;

close all;
imagesc(sigma); colorbar
figure;
imagesc(x,'EraseMode','none',[-1 1]); colorbar
figure;
imagesc(xpca); colorbar