.. _ug_tb_sh_3-1:

************
(3, 1) terms
************

First type of the trilinear terms, in which all three spin operators are associated with
the same site.

.. math::
    C_{3,1}
    \sum_{\substack{\mu, \\ \alpha_1, \\ i_1, i_2, i_3}}
    J^{i_1, i_2, i_3}_{0; \alpha_1, \alpha_1, \alpha_1}
    S_{\mu, \alpha_1}^{i_1}
    S_{\mu, \alpha_1}^{i_2}
    S_{\mu, \alpha_1}^{i_3}

Relevant API
============

*   :py:attr:`magnopy.Convention.c31`

    Convention constant.

*   :py:meth:`magnopy.SpinHamiltonian.add`

    Method to add the parameter to the Hamiltonian.

*   :py:meth:`magnopy.SpinHamiltonian.remove`

    Method to remove the parameter from the Hamiltonian.

*   :py:attr:`magnopy.SpinHamiltonian.p31`

    An iterator over the parameters already added to the Hamiltonian.