function [LL] = Q_step(x, m, S, k, pi, h, flag)
  [num_data, ~] = size(x);
  LL = 0;
  for i = 1:k
    N = mvnpdf(x, m(i, :), S(:, :, i));
    for j = 1:num_data
      LL = LL + h(j, i) * (log(pi(i) + eps) + log(N(j) + eps));
    end
  end
end