Better docs and default value

ctapipe/instrument/trigger.py

@@ -11,9 +11,17 @@ class SoftwareTrigger(TelescopeComponent):
     CTA and still handle the LST hardware stereo trigger and the normal stereo
     trigger correctly.
 
-    LSTs have a hardware trigger, that requires at least two LSTs to have a trigger
-    in each event. Thus, after selecting a subarray, it is needed to
-    - Remove single LST telescope events from events
+    When selecting subarrays from simulations that contain many more telescopes,
+    as is done in all major CTA productions to date, the stereo trigger is not
+    correctly simulated as in that after selecting a realistic subarray, events
+    are still in the data stream where only one telescope of the selected subarray
+    triggered, which would in reality not trigger the stereo trigger.
+
+    An additional complexity is the LST hardware stereo trigger, that forces that
+    an array event has always to contain no or at least two LST telescope events.
+
+    This means that after selectig a subarray, we need to:
+    - Remove LST telescope events from the subarray if only one LST triggered
     - Ignore events with only 1 telescope after this has been applied
     """
 
@@ -26,7 +34,7 @@ class SoftwareTrigger(TelescopeComponent):
     ).tag(config=True)
 
     min_telescopes_of_type = IntTelescopeParameter(
-        default_value=1,
+        default_value=0,
         help=(
             "Minimum number of telescopes required for a specific type."
             " In events with fewer telescopes of that type"
@@ -63,7 +71,7 @@ def __call__(self, event: ArrayEventContainer) -> bool:
             min_tels = self.min_telescopes_of_type.tel[tel_type_str]
 
             # no need to check telescopes for which we have no min requirement
-            if min_tels == 1:
+            if min_tels == 0:
                 continue
 
             tels_with_trigger = set(event.trigger.tels_with_trigger)