Clip post lapse stability (#72)

* clip post lapse stability

* bump patch number

pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "setuptools.build_meta"
 
 [project]
 name = "fsrs"
-version = "4.1.0"
+version = "4.1.1"
 description = "Free Spaced Repetition Scheduler"
 readme = "README.md"
 authors = [{ name = "Jarrett Ye", email = "[email protected]" }]

src/fsrs/fsrs.py

@@ -731,13 +731,22 @@ def _next_stability(
     def _next_forget_stability(
         self, difficulty: float, stability: float, retrievability: float
     ) -> float:
-        return (
+        next_forget_stability_long_term_params = (
             self.parameters[11]
             * math.pow(difficulty, -self.parameters[12])
             * (math.pow(stability + 1, self.parameters[13]) - 1)
             * math.exp((1 - retrievability) * self.parameters[14])
         )
 
+        next_forget_stability_short_term_params = stability / math.exp(
+            self.parameters[17] * self.parameters[18]
+        )
+
+        return min(
+            next_forget_stability_long_term_params,
+            next_forget_stability_short_term_params,
+        )
+
     def _next_recall_stability(
         self, difficulty: float, stability: float, retrievability: float, rating: Rating
     ) -> float: