X_norm = X.copy()
    mu = np.zeros(X.shape[1])
    sigma = np.zeros(X.shape[1])
    # =========================== YOUR CODE HERE =====================
    for j in range(X_norm.shape[1]):
        mu[j] = np.mean(X_norm[:, j])
        sigma[j] = np.std(X_norm[:, j])
        print('sigma[', j, ']:', sigma[j])
        X_norm[:, j] = (X_norm[:, j] - mu[j]) /sigma[j]