Spaced Repetition Algorithms

I'm writing Space Cadet, a REST-based engine to automate Spaced Repetition practice in an minimally opinionated way.

Ultimately, I want anyone who uses this engine to be able to write their own spacing algorithms, but since I'm the guinea pig here, I'll simply implement a few simple ones and use them randomly (and blindly) over time, then after a period I'll look at my recall accuracy to see which algorithm was best suited to me and my memory, if any at all.

Interactive notebook here.

Let's look at a few examples.

Uniform Repetition

Every h hours, for example, h = 72:

Simple Exponential Function

Every h = 2**n (2-to-the-nth) hours where n is the repetition number:

Ebbinghaus' Forgetting Curve

Assuming R >= 0.9 (retention of 90% or better), we can make assumptions about what function models S, or "stability of memory."

If stability increases exponentially, ie. S = e**t (e-to-the-t) where T is time.

If stability is linear, ie. S = et:

If stability shows decreasing marginal returns, ie. S = C*sqrt(t) where C is some constant:

That's all for now. These are very (over)simplified, but ultimately that's inconsequential as I only need them for testing purposes. An ideal algorithm would be a bit more complex (ie. "content aware") and adaptive over time.