Fix/PLS shouldn't exceed last_s (#156)

open-spaced-repetition/fsrs-optimizer#82

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "fsrs"
-version = "0.4.0"
+version = "0.4.1"
 authors = ["Open Spaced Repetition"]
 categories = ["algorithms", "science"]
 edition = "2021"

src/inference.rs

@@ -468,14 +468,14 @@ mod tests {
         let metrics = fsrs.evaluate(items.clone(), |_| true).unwrap();
 
         Data::from([metrics.log_loss, metrics.rmse_bins])
-            .assert_approx_eq(&Data::from([0.201_908, 0.013_894]), 5);
+            .assert_approx_eq(&Data::from([0.201_908, 0.013_964]), 5);
 
         let (self_by_other, other_by_self) = fsrs
             .universal_metrics(items, &DEFAULT_PARAMETERS, |_| true)
             .unwrap();
 
         Data::from([self_by_other, other_by_self])
-            .assert_approx_eq(&Data::from([0.015_987_674, 0.019_702_684]), 5);
+            .assert_approx_eq(&Data::from([0.015_987, 0.019_767]), 5);
         Ok(())
     }
 

src/model.rs

@@ -90,10 +90,13 @@ impl<B: Backend> Model<B> {
         last_d: Tensor<B, 1>,
         r: Tensor<B, 1>,
     ) -> Tensor<B, 1> {
-        self.w.get(11)
+        let new_s = self.w.get(11)
             * last_d.pow(-self.w.get(12))
-            * ((last_s + 1).pow(self.w.get(13)) - 1)
-            * ((-r + 1) * self.w.get(14)).exp()
+            * ((last_s.clone() + 1).pow(self.w.get(13)) - 1)
+            * ((-r + 1) * self.w.get(14)).exp();
+        new_s
+            .clone()
+            .mask_where(last_s.clone().lower(new_s), last_s)
     }
 
     fn mean_reversion(&self, new_d: Tensor<B, 1>) -> Tensor<B, 1> {