memoire

Greatly improve scheduling algorithm
Parent 8cdfc89
John Smith

John Smith commited on 2022-206 08:31:53
Showing 2 changed files, with 19 additions and 8 deletions. 

The scheduling algorithm is now similar to the SM-2-based algorithm
used in Anki, with various simplifications, such as the omission of
a separated "learning" phase.

This change required adding an `Ease` field to each prompt.
Memoire remains backwards-compatible by automatically adding
the default ease to any cards which have no such field.
prompt.lua
View file @ 4bf99c8
... ... 
@@ -2,7 +2,7 @@
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     a prompt consists of prompt text (with an answer-insertion point),
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     a correct answer, the review timestamp, the review delay,
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     counts of successful and failed reviews,
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-    and a creation timestamp
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+    a creation timestamp, and an ease measurement
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     timestamps are seconds from the Unix epoch
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     review delay is in seconds
... ... 
@@ -14,21 +14,22 @@ Prompt.__index = Prompt
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 --[[
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     the answer-insertion point is indicated with a "%A" in the prompt text
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 ]]
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-function Prompt:new(pt, ca, rts, rd, sc, fc, ct)
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+function Prompt:new(pt, ca, rts, rd, sc, fc, ct, ez)
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     local o = {}
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     setmetatable(o, self)
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     o.text = pt
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     o.ans = ca
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     o.time = tonumber(rts)
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     o.delay = tonumber(rd)
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-    o.succ = sc
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-    o.fail = fc
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+    o.succ = tonumber(sc)
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+    o.fail = tonumber(fc)
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     o.created = ct
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+    o.ease = tonumber(ez)
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     return o
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 end
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 function Prompt:__tostring()
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-    return string.format("\"%s\" (\"%s\") %d+%d %d/%d", self.text, self.ans, self.time, self.delay, self.succ, self.fail)
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+    return string.format("\"%s\" (\"%s\") %d -> %d+%d*%d %d/%d", self.text, self.ans, self.created, self.time, self.delay, self.ease, self.succ, self.fail)
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 end
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 --[[
... ... 
@@ -60,7 +61,8 @@ function Prompt:fromrecs(recs)
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                     (rec.LastDelay or {})[ctr],
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                     (rec.Successes or {})[ctr],
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                     (rec.Failures or {})[ctr],
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-                    (rec.Created or {})[1]
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+                    (rec.Created or {})[1],
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+                    (rec.Ease or {})[ctr] or "2.5"
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                 ))
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                 m, n = opt:find("%{[^%}]+%}", n)
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                 ctr = ctr + 1
... ... 
@@ -80,7 +82,7 @@ function Prompt:torec(prompts)
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         return {}
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     end
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     local fspt = prompts[1]:spt()
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-    local ret = { PromptText = { fspt }, LastReview = {}, LastDelay = {}, Successes = {}, Failures = {} }
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+    local ret = { PromptText = { fspt }, LastReview = {}, LastDelay = {}, Successes = {}, Failures = {}, Ease = {} }
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     if prompts[1].created then
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         ret.Created = { prompts[1].created }
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     end
... ... 
@@ -93,6 +95,7 @@ function Prompt:torec(prompts)
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         ret.LastDelay[i] = pr.delay
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         ret.Successes[i] = pr.succ
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         ret.Failures[i] = pr.fail
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+        ret.Ease[i] = pr.ease
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     end
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     return ret
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 end
review.lua
View file @ 4bf99c8
... ... 
@@ -10,7 +10,14 @@
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 local function schedule(prompt, revtime, revsucc, conf)
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     if revsucc and revsucc > 0 then
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         local ad = revtime - (prompt.time or revtime)
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-        return (conf:get("DelayRatio") or 2.5) ^ revsucc * (ad + math.max(40000 - 0.5 * ad, 0))
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+        local adm = ad + math.max(40000 - 0.5 * ad, 0)
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+        -- SM2, as explained by Bjornstad
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+        -- https://controlaltbackspace.org/memory/spaced-repetition-from-the-ground-up/
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+        if revsucc < 0.8 then
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+            return (conf:get("HardRatio") or 1.2) * revsucc * 2 * adm
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+        else
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+            return prompt.ease * (1 + 2 * ((conf:get("EasyRatio") or 1.3) - 1) * (revsucc - 1)) * adm
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+        end
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     else
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         return 15
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     end
... ... 
@@ -29,6 +36,7 @@ local function update(prompt, revtime, revsucc, conf)
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     -- allowed random variation, as a fraction of the "optimal" duration
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     local ARV = conf:get("AllowedRandomVariation") or 0.1
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     prompt.delay = schedule(prompt, revtime, revsucc, conf) * ((1 - ARV) + 2 * ARV * math.random())
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+    prompt.ease = prompt.ease + ({ -0.2, -0.15, 0, 0.15 })[2 * revsucc + 1]
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     prompt.time = revtime
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 end
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