Specifying symmetry
===================

YASTN specifies symmetry through any object that is a plain Python module or class which defines

    #. ``SYM_ID`` string label specyfying the symmetry

    #. ``NSYM`` number of elements in the charge vector. For example, NSYM=1
       for :math:`U(1)` or :math:`Z_2` group. For product groups such
       as :math:`U(1)\times U(1)`, NSYM=2

    #. ``fuse`` function that specifies the addition of charges

.. automodule:: yastn.sym.sym_abelian
    :members: sym_abelian

Example symmetries defined in YASTN
-----------------------------------

* :math:`U(1)` symmetry

.. literalinclude:: /../../yastn/sym/sym_U1.py
    :pyobject: sym_U1

* :math:`Z_2` symmetry

.. literalinclude:: /../../yastn/sym/sym_Z2.py
    :pyobject: sym_Z2

* :math:`Z_2\times U(1)`

.. literalinclude:: /../../yastn/sym/sym_Z2xU1.py
    :pyobject: sym_Z2xU1