taul = tau(i);
    err = 0;
    for k = 0:N-1
        xtest = X([idxperm([floor(m / N * k + 1) : floor(m / N * (k + 1))])], :);
        ytest = Y([idxperm([floor(m / N * k + 1) : floor(m / N * (k + 1))])], 1);
        xtrain = vertcat(X([idxperm(1: [floor(m / N * k + 1) - 1])], :), X([idxperm([floor(m / N * (k + 1)) + 1 : m])], :));
        ytrain = vertcat(Y([idxperm(1: [floor(m / N * k + 1) - 1])], 1), Y([idxperm([floor(m / N * (k + 1)) + 1 : m])], 1));
        [p, q] = size(xtest);
        err2 = 0;
        for r = 1:p
            pred_Y = q6_predict(xtrain, ytrain, xtest(r, :)', taul);
            err2 = err2 + q5_mse(pred_Y, ytest(r));
        end
        err = err + err2/p;
    end
    error(1, i) = err/N;