@staticmethod
def _get_atoms(linkage, element):
    """
        Getting the atoms included in an element from a linkage object

        Atoms are the basic assets in a portfolio and not clusters.

        :param linkage: (np.array) Global linkage object
        :param element: (int) Element id to get atoms from
        :return: (list) Set of atoms
        """
    element_list = [element]
    while True:
        item_ = max(element_list)
        if item_ > linkage.shape[0]:
            element_list.remove(item_)
            element_list.append(linkage['i0'][item_ - linkage.shape[0] - 1])
            element_list.append(linkage['i1'][item_ - linkage.shape[0] - 1])
        else:
            break
    return element_list
