def fractional_to_cartesian(basis_vectors, lattice_vectors):
    """Convert fractional coordinates to cartesian coordinates.

    :param basis_vectors:
        N by 3 numpy array of basis vectors
    :type basis_vectors:
        np.ndarray
    :param lattice_vectors:
        3 by 3 numpy array of lattice vectors [a1, a2, a3]
    :type lattice_vectors:
        np.ndarray
    :return:
        N by 3 numpy array of cartesiann coordinates
    :rtype:
        np.ndarray
    """
    return basis_vectors.dot(lattice_vectors)