Add parameters to the model and initialize with given values.

def _set_parameters(self, parameters):
        """Add parameters to the model and initialize with given values."""
        for theta in self.variables['theta']:
            val = 1.0
            # TODO: improve approach for initializing parameters.
            if parameters is not None:
                if theta.name in parameters:
                    val = parameters[theta.name]
            # Add parameter.
            
            self.link_parameters(Param(theta.name, val, None))