Simulating autonomous systems without dummy input for u

Fixes #183

do_mpc/simulator.py

@@ -439,7 +439,7 @@ def simulate(self):
 
         return x_new
 
-    def make_step(self, u0, v0=None, w0=None):
+    def make_step(self, u0=None, v0=None, w0=None):
         """Main method of the simulator class during control runtime. This method is called at each timestep
         and computes the next state or the current control input :py:obj:`u0`. The method returns the resulting measurement,
         as defined in :py:class:`do_mpc.model.Model.set_meas`.
@@ -455,7 +455,7 @@ def make_step(self, u0, v0=None, w0=None):
         The method prepares the simulator by setting the current parameters, calls :py:func:`simulator.simulate`
         and updates the :py:class:`do_mpc.data` object.
 
-        :param u0: Current input to the system.
+        :param u0: Current input to the system. Optional parameter for autonomous systems.
         :type u0: numpy.ndarray
 
         :param v0: Additive measurement noise
@@ -467,6 +467,11 @@ def make_step(self, u0, v0=None, w0=None):
         :return: y_next
         :rtype: numpy.ndarray
         """
+        # Generate dummy input if system is autnomous
+        if u0 is None:
+            assert self.model.n_u == 0, 'No input u0 provided. Please provide an input u0.'
+            u0 = self.model._u(0)
+
         assert self.flags['setup'] == True, 'Simulator is not setup. Call simulator.setup() first.'
         assert isinstance(u0, (np.ndarray, casadi.DM, structure3.DMStruct)), 'u0 is wrong input type. You have: {}'.format(type(u0))
         assert u0.shape == self.model._u.shape, 'u0 has incorrect shape. You have: {}, expected: {}'.format(u0.shape, self.model._u.shape)