[Fix] Docstrings for get_longitudinal_twiss

Add an explaination how to get non zero longitudinal cs_invariant

mbtrack2/tracking/particles.py

@@ -299,6 +299,9 @@ class Bunch:
         """
         Return the average Courant-Snyder invariant of each plane.
 
+        To get non-zero longitudinal Courant-Snyder invariant, the longitudinal
+        Twiss parameters need to be computed using the ring.get_longitudinal_twiss
+        method.
         """
         Jx = ((self.ring.optics.local_gamma[0] * self["x"]**2) +
               (2 * self.ring.optics.local_alpha[0] * self["x"]) * self["xp"] +

mbtrack2/tracking/synchrotron.py

@@ -459,17 +459,18 @@ class Synchrotron:
             Harmonics of the cavities to consider.
             Default is None.
         add : bool, optional
-            If True, 
-            
+            If True, add the computed longitudinal Twiss parameters as class
+            arguements.
+
         Usage
         -----
-        - If a single voltage value is given, assume a single RF system set at 
+        - If a single voltage value is given, assume a single RF system set at
         the synchronous phase.
-        - If a single pair of voltage/phase value is given, assume a single RF 
+        - If a single pair of voltage/phase value is given, assume a single RF
         system at this setting.
-        - Otherwise, compute the synchrotron tune for a multi-harmonic RF 
+        - Otherwise, compute the synchrotron tune for a multi-harmonic RF
         system.
-            
+
         Returns
         -------
         tuneS : float