Fix parallel Monte Carlo simulation showing incorrect iteration count (#885)

* Fix parallel Monte Carlo iteration count display to show monotonically increasing completed count

Co-authored-by: Gui-FernandesBR <[email protected]>

* Add PR #806 to CHANGELOG.md

Co-authored-by: Gui-FernandesBR <[email protected]>

---------

Co-authored-by: copilot-swe-agent[bot] <[email protected]>
Co-authored-by: Gui-FernandesBR <[email protected]>

Author: Copilot

CHANGELOG.md

@@ -45,6 +45,7 @@ Attention: The newest changes should be on top -->
 
 ### Fixed
 
+- BUG: Fix parallel Monte Carlo simulation showing incorrect iteration count [#806](https://github.com/RocketPy-Team/RocketPy/pull/806)
 - BUG: Fix CSV column header spacing in FlightDataExporter [#864](https://github.com/RocketPy-Team/RocketPy/issues/864)
 
 

rocketpy/simulation/monte_carlo.py

@@ -292,7 +292,7 @@ def __run_in_serial(self):
                 with open(self.output_file, "a", encoding="utf-8") as f:
                     f.write(outputs_json)
 
-                sim_monitor.print_update_status(sim_monitor.count)
+                sim_monitor.print_update_status()
 
             sim_monitor.print_final_status()
 
@@ -430,7 +430,7 @@ def __sim_producer(self, seed, sim_monitor, mutex, error_event):  # pylint: disa
                     with open(self.output_file, "a", encoding="utf-8") as f:
                         f.write(outputs_json)
 
-                    sim_monitor.print_update_status(sim_idx)
+                    sim_monitor.print_update_status()
                 finally:
                     mutex.release()
 
@@ -1208,6 +1208,7 @@ def __init__(self, initial_count, n_simulations, start_time):
         self.count = initial_count
         self.n_simulations = n_simulations
         self.start_time = start_time
+        self.completed_count = 0
 
     def keep_simulating(self):
         return self.count < self.n_simulations
@@ -1216,25 +1217,24 @@ def increment(self):
         self.count += 1
         return self.count
 
-    def print_update_status(self, sim_idx):
+    def print_update_status(self):
         """Prints a message on the same line as the previous one and replaces
         the previous message with the new one, deleting the extra characters
-        from the previous message.
-
-        Parameters
-        ----------
-        sim_idx : int
-            Index of the current simulation.
+        from the previous message. This method increments the completed_count
+        to track how many simulations have finished (thread-safe when called
+        within a mutex-protected section).
 
         Returns
         -------
         None
         """
+        self.completed_count += 1
 
-        average_time = (time() - self.start_time) / (self.count - self.initial_count)
-        estimated_time = int((self.n_simulations - self.count) * average_time)
+        average_time = (time() - self.start_time) / self.completed_count
+        remaining = self.n_simulations - self.initial_count - self.completed_count
+        estimated_time = int(remaining * average_time)
 
-        msg = f"Current iteration: {sim_idx:06d}"
+        msg = f"Iterations completed: {self.completed_count:06d}"
         msg += f" | Average Time per Iteration: {average_time:.3f} s"
         msg += f" | Estimated time left: {estimated_time} s"