refactor : very small but remove if, in forward dynamics to handle an…

…d switch between cases.

bioptim/dynamics/dynamics_functions.py

@@ -1129,19 +1129,17 @@ def forward_dynamics(
         else:
             qdot_var_mapping = BiMapping([i for i in range(qdot.shape[0])], [i for i in range(qdot.shape[0])]).to_first
 
-        if external_forces is None:
-            if with_contact:
-                qddot = nlp.model.constrained_forward_dynamics(q, qdot, tau)
-            else:
-                qddot = nlp.model.forward_dynamics(q, qdot, tau)
+        dynamics_functions = {
+            (True, True): nlp.model.constrained_forward_dynamics,
+            (True, False): nlp.model.forward_dynamics,
+            (False, True): lambda q, qdot, tau: nlp.model.constrained_forward_dynamics(q, qdot, tau, external_forces),
+            (False, False): lambda q, qdot, tau: nlp.model.forward_dynamics(q, qdot, tau, external_forces),
+        }
 
-            return qdot_var_mapping.map(qddot)
-        else:
-            if with_contact:
-                qddot = nlp.model.constrained_forward_dynamics(q, qdot, tau, external_forces)
-            else:
-                qddot = nlp.model.forward_dynamics(q, qdot, tau, external_forces)
-            return qdot_var_mapping.map(qddot)
+        dynamics_function = dynamics_functions[(external_forces is None, with_contact)]
+
+        qddot = dynamics_function(q, qdot, tau)
+        return qdot_var_mapping.map(qddot)
 
     @staticmethod
     def inverse_dynamics(