def METHOD_NAME(self, ttype):
    """
    Sets the type of equation to use for evolving the cold electron density.
    :param int ttype: Flag indicating how to evolve the cold electron density.
    """
    if ttype == TYPE_PRESCRIBED:
        self.type = ttype
    elif ttype == TYPE_SELFCONSISTENT:
        self.type = ttype
    else:
        raise EquationException("n_cold: Unrecognized cold electron density type: {}".format(self.type))