:orphan: .. _altering_param_dict: ************************************************* Changing Composite Model Parameters ************************************************* All Halotools composite models have a ``param_dict`` attribute, a python dictionary storing the complete collection of tunable parameters of the model. By altering the values of stored in ``param_dict``, you change the behavior of the model. If you are running an MCMC-type likelihood analysis, your walker should explore the parameter space of (some subset of) the parameters stored in the model ``param_dict``. For information about how changes in ``param_dict`` propagate through Halotools source code, see :ref:`param_dict_mechanism` section of the :ref:`composite_model_constructor_bookkeeping_mechanisms` page in the documentation.