Class FSRSAlgorithm

Get the parameters of the algorithm.

Set the parameters of the algorithm.

If fuzzing is disabled or ivl is less than 2.5, it returns the original interval.

See

https://github.com/open-spaced-repetition/fsrs4anki/wiki/The-Algorithm#fsrs-45

The formula used is: $$I(r,s) = (r^{\frac{1}{DECAY}} - 1) / FACTOR \times s$$

Throws

Requested retention rate should be in the range (0,1]

The formula used is : $$\min \lbrace \max \lbrace D_0,1 \rbrace,10\rbrace$$

The formula used is : $$R(t,S) = (1 + \text{FACTOR} \times \frac{t}{9 \cdot S})^{\text{DECAY}}$$

The formula used is : $$D_0(G) = w_4 - e^{(G-1) \cdot w_5} + 1 $$ $$D_0 = \min \lbrace \max \lbrace D_0(G),1 \rbrace,10 \rbrace$$ where the $$D_0(1)=w_4$$ when the first rating is good.

The formula used is : $$ S_0(G) = w_{G-1}$$ $$S_0 = \max \lbrace S_0,0.1\rbrace $$

See

https://github.com/open-spaced-repetition/fsrs4anki/issues/697

The formula used is : $$w_7 \cdot \text{init} +(1 - w_7) \cdot \text{current}$$

The formula used is : $$\text{delta}_d = -w_6 \cdot (g - 3)$$ $$\text{next}_d = D + \text{linear damping}(\text{delta}_d , D)$$ $$D^\prime(D,R) = w_7 \cdot D_0(4) +(1 - w_7) \cdot \text{next}_d$$

The formula used is : $$S^\prime_f(D,S,R) = w_{11}\cdot D^{-w_{12}}\cdot ((S+1)^{w_{13}}-1) \cdot e^{w_{14}\cdot(1-R)}$$ enable_short_term = true : $$S^\prime_f \in \min \lbrace \max \lbrace S^\prime_f,0.01\rbrace, \frac{S}{e^{w_{17} \cdot w_{18}}} \rbrace$$ enable_short_term = false : $$S^\prime_f \in \min \lbrace \max \lbrace S^\prime_f,0.01\rbrace, S \rbrace$$

See

The formula used is : FSRSAlgorithm.calculate_interval_modifier

The formula used is : $$S^\prime_r(D,S,R,G) = S\cdot(e^{w_8}\cdot (11-D)\cdot S^{-w_9}\cdot(e^{w_{10}\cdot(1-R)}-1)\cdot w_{15}(\text{if} G=2) \cdot w_{16}(\text{if} G=4)+1)$$

The formula used is : $$S^\prime_s(S,G) = S \cdot e^{w_{17} \cdot (G-3+w_{18})}$$