@abc.abstractmethod<EOL><INDENT>def dstationarystate(self, param):<DEDENT>
pass<EOL>
Derivative of `stationarystate` with respect to `param`.

            Args:
                `param` (string in `freeparams`)

            Returns:
                `dstationarystate` (`numpy.ndarray` of floats or zero)
                    If `param` is a float, then `dstationarystate[r][x]`
                    is derivative of `stationarystate[r][x]` with respect
                    to `param`. If `param` is an array, then
                    `dstationarystate[i][r][x]` is derivative of
                    `stationarystate[r][x]` with respect to `param[i]`.