Protected Optional_seedThe formula used is : $$R(t,S) = (1 + \text{FACTOR} \times \frac{t}{9 \cdot S})^{\text{DECAY}}$$
t days since the last review
Stability (interval when R=90%)
r Retrievability (probability of recall)
ProtectedintervalProtectedparamGet the parameters of the algorithm.
If fuzzing is disabled or ivl is less than 2.5, it returns the original interval.
The interval to be fuzzed.
t days since the last review
0<request_retention<=1,Requested retention rate
https://github.com/open-spaced-repetition/fsrs4anki/wiki/The-Algorithm#fsrs-5
The formula used is: $$I(r,s) = (r^{\frac{1}{DECAY}} - 1) / FACTOR \times s$$
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.
Grade (rating at Anki) [1.again,2.hard,3.good,4.easy]
Difficulty $$D \in [1,10]$$
The formula used is : $$ S_0(G) = w_{G-1}$$ $$S_0 = \max \lbrace S_0,0.1\rbrace $$
Grade (rating at Anki) [1.again,2.hard,3.good,4.easy]
Stability (interval when R=90%)
The formula used is : $$w_7 \cdot \text{init} +(1 - w_7) \cdot \text{current}$$
$$w_2 : D_0(3) = w_2 + (R-2) \cdot w_3= w_2$$
$$D - w_6 \cdot (R - 2)$$
difficulty
The formula used is : $$\text{delta}_d = -w_6 \cdot (g - 3)$$ $$\text{next}_d = D + \text{linear damping}(\text{delta}_d , D)$$ $$D^\prime(D,R) = w_7 \cdot D_0(4) +(1 - w_7) \cdot \text{next}_d$$
Difficulty $$D \in [1,10]$$
Grade (rating at Anki) [1.again,2.hard,3.good,4.easy]
$$\text{next}_D$$
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 : $$S^\prime_f \in \min \lbrace \max \lbrace S^\prime_f,0.01\rbrace, S \rbrace$$
Difficulty D \in [1,10]
Stability (interval when R=90%)
Retrievability (probability of recall)
S^\prime_f new stability after forgetting
Stability (interval when R=90%)
t days since the last review
The formula used is : FSRSAlgorithm.calculate_interval_modifier
The formula used is : $$S^\prime_r(D,S,R,G) = S\cdot(e^{w_8}\cdot (11-D)\cdot S^{-w_9}\cdot(e^{w_{10}\cdot(1-R)}-1)\cdot w_{15}(\text{if} G=2) \cdot w_{16}(\text{if} G=4)+1)$$
Difficulty D \in [1,10]
Stability (interval when R=90%)
Retrievability (probability of recall)
Grade (Rating[0.again,1.hard,2.good,3.easy])
S^\prime_r new stability after recall
The formula used is : $$S^\prime_s(S,G) = S \cdot e^{w_{17} \cdot (G-3+w_{18})}$$
Stability (interval when R=90%)
Grade (Rating[0.again,1.hard,2.good,3.easy])
Calculates the next state of memory based on the current state, time elapsed, and grade.
The current state of memory, which can be null.
The time elapsed since the last review.
Grade (Rating[0.Manual,1.Again,2.Hard,3.Good,4.Easy])
The next state of memory with updated difficulty and stability.
Protectedparams_
See
https://github.com/open-spaced-repetition/fsrs4anki/wiki/The-Algorithm#fsrs-45