function y=ppe(x, a, m, cm)
% evaluate the normalazation factor of the densities

[dimx,lenx] = size(x);
N = length(a);

y = zeros(1, lenx);

for k = 1:N
    y = y + a(k)*gau(x, m(:,k), cm(:, (k-1)*dimx+1 : k*dimx));
end