FSRS-5 (#52)

* start work on fsrs-5 * implement short term stability function * update difficulty and stability in (re)learning step * modify tests * modify custom scheduler example in readme to use 19 parameters instead of 17 for fsrs5 * bump major version
open-spaced-repetition · Aug 22, 2024 · b91d3d0 · b91d3d0
1 parent 3087e1c
commit b91d3d0
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Showing 5 changed files with 143 additions and 166 deletions.
diff --git a/README.md b/README.md
@@ -88,23 +88,25 @@ You can initialize the FSRS scheduler with your own custom weights as well as de
 ```python
 f = FSRS(
     w=(
-        1.14,
-        1.01,
-        5.44,
-        14.67,
-        5.3024,
-        1.5662,
-        1.2503,
-        0.0028,
-        1.5489,
-        0.1763,
-        0.9953,
-        2.7473,
-        0.0179,
-        0.3105,
-        0.3976,
-        0.0,
-        2.0902,
+        0.4197,
+        1.1869,
+        3.0412,
+        15.2441,
+        7.1434,
+        0.6477,
+        1.0007,
+        0.0674,
+        1.6597,
+        0.1712,
+        1.1178,
+        2.0225,
+        0.0904,
+        0.3025,
+        2.1214,
+        0.2498,
+        2.9466,
+        0.4891,
+        0.6468,
     ),
     request_retention=0.85,
     maximum_interval=3650,

diff --git a/pyproject.toml b/pyproject.toml
@@ -4,7 +4,7 @@ build-backend = "setuptools.build_meta"
 
 [project]
 name = "fsrs"
-version = "2.5.1"
+version = "3.0.0"
 description = "Free Spaced Repetition Scheduler"
 readme = "README.md"
 authors = [{ name = "Jarrett Ye", email = "[email protected]" }]

diff --git a/src/fsrs/fsrs.py b/src/fsrs/fsrs.py
@@ -58,17 +58,22 @@ def repeat(
             s.easy.scheduled_days = easy_interval
             s.easy.due = now + timedelta(days=easy_interval)
         elif card.state == State.Learning or card.state == State.Relearning:
+            interval = card.elapsed_days
+            last_d = card.difficulty
+            last_s = card.stability
+            retrievability = self.forgetting_curve(interval, last_s)
+            self.next_ds(s, last_d, last_s, retrievability, card.state)
+
             hard_interval = 0
             good_interval = self.next_interval(s.good.stability)
             easy_interval = max(self.next_interval(s.easy.stability), good_interval + 1)
-
             s.schedule(now, hard_interval, good_interval, easy_interval)
         elif card.state == State.Review:
             interval = card.elapsed_days
             last_d = card.difficulty
             last_s = card.stability
             retrievability = self.forgetting_curve(interval, last_s)
-            self.next_ds(s, last_d, last_s, retrievability)
+            self.next_ds(s, last_d, last_s, retrievability, card.state)
 
             hard_interval = self.next_interval(s.hard.stability)
             good_interval = self.next_interval(s.good.stability)
@@ -89,28 +94,45 @@ def init_ds(self, s: SchedulingCards) -> None:
         s.easy.stability = self.init_stability(Rating.Easy)
 
     def next_ds(
-        self, s: SchedulingCards, last_d: float, last_s: float, retrievability: float
+        self,
+        s: SchedulingCards,
+        last_d: float,
+        last_s: float,
+        retrievability: float,
+        state,
     ):
         s.again.difficulty = self.next_difficulty(last_d, Rating.Again)
-        s.again.stability = self.next_forget_stability(last_d, last_s, retrievability)
         s.hard.difficulty = self.next_difficulty(last_d, Rating.Hard)
-        s.hard.stability = self.next_recall_stability(
-            last_d, last_s, retrievability, Rating.Hard
-        )
         s.good.difficulty = self.next_difficulty(last_d, Rating.Good)
-        s.good.stability = self.next_recall_stability(
-            last_d, last_s, retrievability, Rating.Good
-        )
         s.easy.difficulty = self.next_difficulty(last_d, Rating.Easy)
-        s.easy.stability = self.next_recall_stability(
-            last_d, last_s, retrievability, Rating.Easy
-        )
+
+        if state == State.Learning or state == State.Relearning:
+            # compute short term stabilities
+            s.again.stability = self.short_term_stability(last_s, Rating.Again)
+            s.hard.stability = self.short_term_stability(last_s, Rating.Hard)
+            s.good.stability = self.short_term_stability(last_s, Rating.Good)
+            s.easy.stability = self.short_term_stability(last_s, Rating.Easy)
+
+        elif state == State.Review:
+            s.again.stability = self.next_forget_stability(
+                last_d, last_s, retrievability
+            )
+            s.hard.stability = self.next_recall_stability(
+                last_d, last_s, retrievability, Rating.Hard
+            )
+            s.good.stability = self.next_recall_stability(
+                last_d, last_s, retrievability, Rating.Good
+            )
+            s.easy.stability = self.next_recall_stability(
+                last_d, last_s, retrievability, Rating.Easy
+            )
 
     def init_stability(self, r: int) -> float:
         return max(self.p.w[r - 1], 0.1)
 
     def init_difficulty(self, r: int) -> float:
-        return min(max(self.p.w[4] - self.p.w[5] * (r - 3), 1), 10)
+        # compute initial difficulty and clamp it between 1 and 10
+        return min(max(self.p.w[4] - math.exp(self.p.w[5] * (r - 1)) + 1, 1), 10)
 
     def forgetting_curve(self, elapsed_days: int, stability: float) -> float:
         return (1 + self.FACTOR * elapsed_days / stability) ** self.DECAY
@@ -123,7 +145,13 @@ def next_interval(self, s: float) -> int:
 
     def next_difficulty(self, d: float, r: int) -> float:
         next_d = d - self.p.w[6] * (r - 3)
-        return min(max(self.mean_reversion(self.p.w[4], next_d), 1), 10)
+
+        return min(
+            max(self.mean_reversion(self.init_difficulty(Rating.Easy), next_d), 1), 10
+        )
+
+    def short_term_stability(self, stability, rating):
+        return stability * math.exp(self.p.w[17] * (rating - 3 + self.p.w[18]))
 
     def mean_reversion(self, init: float, current: float) -> float:
         return self.p.w[7] * init + (1 - self.p.w[7]) * current

diff --git a/src/fsrs/models.py b/src/fsrs/models.py
@@ -278,23 +278,25 @@ def __init__(
             w
             if w is not None
             else (
-                0.4872,
-                1.4003,
-                3.7145,
-                13.8206,
-                5.1618,
-                1.2298,
-                0.8975,
-                0.031,
-                1.6474,
-                0.1367,
-                1.0461,
-                2.1072,
-                0.0793,
-                0.3246,
-                1.587,
-                0.2272,
-                2.8755,
+                0.4072,
+                1.1829,
+                3.1262,
+                15.4722,
+                7.2102,
+                0.5316,
+                1.0651,
+                0.0234,
+                1.616,
+                0.1544,
+                1.0824,
+                1.9813,
+                0.0953,
+                0.2975,
+                2.2042,
+                0.2407,
+                2.9466,
+                0.5034,
+                0.6567,
             )
         )
         self.request_retention = (
-Original file line number
+Diff line change
@@ Expand Up / @@ -278,23 +278,25 @@ def __init__( @@
                 w
                 if w is not None
                 else (
-.4872,
-.4003,
-.7145,
-.8206,
-.1618,
-.2298,
-.8975,
-.031,
-.6474,
-.1367,
-.0461,
-.1072,
-.0793,
-.3246,
-.587,
-.2272,
-.8755,
+.4072,
+.1829,
+.1262,
+.4722,
+.2102,
+.5316,
+.0651,
+.0234,
+.616,
+.1544,
+.0824,
+.9813,
+.0953,
+.2975,
+.2042,
+.2407,
+.9466,
+.5034,
+.6567,
                 )
             )
             self.request_retention = (
@@ Expand Down @@