def normalize(X, m, s):
    """normalize: normalizes (standardizes) a matrix

    Args:
        X:  is the numpy.ndarray of shape (d, nx) to normalize
            d is the number of data points
            nx is the number of features

        m: is a numpy.ndarray of shape (nx,) that contains
            the mean of all features of X
        s: is a numpy.ndarray of shape (nx,) that contains
            the standard deviation of all features of X

    Returns
        The normalized X matrix
    """
    return (X - m) / s