Fix maia paper and only eval half the positions

Author: daniel-monroe

src/constants/common.ts

@@ -1,6 +1,9 @@
+// The Maia model is only run at multiples of 200 Elo. The intermediate levels
+// (200n + 100, e.g. 700, 900, ...) are not selectable; they only appear in the
+// "Moves by Rating" graph, where they are linearly interpolated.
 export const MAIA_MODELS = Array.from(
-  { length: 21 },
-  (_, i) => `maia_kdd_${600 + i * 100}`,
+  { length: 11 },
+  (_, i) => `maia_kdd_${600 + i * 200}`,
 )
 
 export const MAIA_RATINGS = MAIA_MODELS.map((m) =>

src/hooks/useAnalysisController/useMoveRecommendations.ts

@@ -1,6 +1,6 @@
 import { useMemo } from 'react'
 import { Chess } from 'chess.ts'
-import { MAIA_MODELS } from 'src/constants/common'
+import { MAIA_MODELS, MAIA_RATINGS } from 'src/constants/common'
 import { GameNode, MaiaEvaluation, StockfishEvaluation } from 'src/types'
 import { sortStockfishMoves } from './utils'
 
@@ -105,15 +105,27 @@ export const useMoveRecommendations = (
       }
     }
 
+    // Maia is only evaluated at multiples of 200 Elo (MAIA_MODELS). The graph is
+    // drawn at a finer 100-Elo resolution: evaluated levels use their real policy
+    // and the intermediate levels (200n + 100) are linearly interpolated from
+    // their two neighbours.
+    const probabilityAt = (rating: number, move: string): number =>
+      (maia[`maia_kdd_${rating}`]?.policy?.[move] || 0) * 100
+
+    const minRating = MAIA_RATINGS[0]
+    const maxRating = MAIA_RATINGS[MAIA_RATINGS.length - 1]
+
     const data = []
-    for (const rating of MAIA_MODELS) {
-      const entry: { [key: string]: number } = {
-        rating: parseInt(rating.replace('maia_kdd_', '')),
-      }
+    for (let rating = minRating; rating <= maxRating; rating += 100) {
+      const entry: { [key: string]: number } = { rating }
+      const isEvaluated = rating % 200 === 0
 
       for (const move of candidates) {
-        const probability = (maia[rating]?.policy?.[move[0]] || 0) * 100
-        entry[move[1]] = probability
+        entry[move[1]] = isEvaluated
+          ? probabilityAt(rating, move[0])
+          : (probabilityAt(rating - 100, move[0]) +
+              probabilityAt(rating + 100, move[0])) /
+            2
       }
 
       data.push(entry)