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Calculate and display Elo change on server #7960

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merged 5 commits into from
Jan 31, 2021
Merged

Calculate and display Elo change on server #7960

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3d0808e
Server: Move Elo calculation into separate file
Jan 29, 2021
c570634
Server: Calculate Elo for display before updating ladder on loginserver
Jan 29, 2021
c52934a
Fix linting errors
Jan 29, 2021
2c8d3c5
Server: separate Elo calculation for main server
Jan 29, 2021
ba216fb
Remove unnecessary code following PR feedback
DylanSp Jan 31, 2021
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56 changes: 32 additions & 24 deletions server/ladders-local.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -172,30 +172,7 @@ export class LadderStore {
updateRow(row: LadderRow, score: number, foeElo: number) {
let elo = row[1];

// The K factor determines how much your Elo changes when you win or
// lose games. Larger K means more change.
// In the "original" Elo, K is constant, but it's common for K to
// get smaller as your rating goes up
let K = 50;

// dynamic K-scaling (optional)
if (elo < 1200) {
if (score < 0.5) {
K = 10 + (elo - 1000) * 40 / 200;
} else if (score > 0.5) {
K = 90 - (elo - 1000) * 40 / 200;
}
} else if (elo > 1350 && elo <= 1600) {
K = 40;
} else {
K = 32;
}

// main Elo formula
const E = 1 / (1 + Math.pow(10, (foeElo - elo) / 400));
elo += K * (score - E);

if (elo < 1000) elo = 1000;
elo = this.calculateElo(elo, score, foeElo);

row[1] = elo;
if (score > 0.6) {
Expand Down Expand Up @@ -334,4 +311,35 @@ export class LadderStore {
}
return Promise.all(ratings);
}

/**
* Calculates Elo based on a match result
*/
private calculateElo(previousUserElo: number, score: number, foeElo: number): number {
// The K factor determines how much your Elo changes when you win or
// lose games. Larger K means more change.
// In the "original" Elo, K is constant, but it's common for K to
// get smaller as your rating goes up
let K = 50;

// dynamic K-scaling (optional)
if (previousUserElo < 1200) {
if (score < 0.5) {
K = 10 + (previousUserElo - 1000) * 40 / 200;
} else if (score > 0.5) {
K = 90 - (previousUserElo - 1000) * 40 / 200;
}
} else if (previousUserElo > 1350 && previousUserElo <= 1600) {
K = 40;
} else {
K = 32;
}

// main Elo formula
const E = 1 / (1 + Math.pow(10, (foeElo - previousUserElo) / 400));

const newElo = previousUserElo + K * (score - E);

return Math.max(newElo, 1000);
}
}
101 changes: 61 additions & 40 deletions server/ladders-remote.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -70,25 +70,43 @@ export class LadderStore {
const formatid = this.formatid;
const p1 = Users.getExact(p1name);
const p2 = Users.getExact(p2name);
room.update();
room.send(`||Ladder updating...`);
const [data, error] = await LoginServer.request('ladderupdate', {

const ladderUpdatePromise = LoginServer.request('ladderupdate', {
p1: p1name,
p2: p2name,
score: p1score,
format: formatid,
});
Comment on lines +74 to 79
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Could this just be moved down to where await ladderUpdatePromise is?

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This allows the loginserver's processing to happen concurrently with the server running and displaying the Elo changes. It's admittedly a small optimization, given that the Elo calc doesn't take much time; up to you if you want to change it.

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Oh, I see! I think this is fine.


// calculate new Elo scores and display to room while loginserver updates the ladder
const [p1OldElo, p2OldElo] = (await Promise.all([this.getRating(p1!.id), this.getRating(p2!.id)])).map(Math.round);
const p1NewElo = Math.round(this.calculateElo(p1OldElo, p1score, p2OldElo));
const p2NewElo = Math.round(this.calculateElo(p2OldElo, 1 - p1score, p1OldElo));

const p1Act = (p1score > 0.9 ? `winning` : (p1score < 0.1 ? `losing` : `tying`));
let p1Reasons = `${p1NewElo - p1OldElo} for ${p1Act}`;
if (!p1Reasons.startsWith('-')) p1Reasons = '+' + p1Reasons;
room.addRaw(Utils.html`${p1name}'s rating: ${p1OldElo} &rarr; <strong>${p1NewElo}</strong><br />(${p1Reasons})`);

const p2Act = (p1score > 0.9 || p1score < 0 ? `losing` : (p1score < 0.1 ? `winning` : `tying`));
let p2Reasons = `${p2NewElo - p2OldElo} for ${p2Act}`;
if (!p2Reasons.startsWith('-')) p2Reasons = '+' + p2Reasons;
room.addRaw(Utils.html`${p2name}'s rating: ${p2OldElo} &rarr; <strong>${p2NewElo}</strong><br />(${p2Reasons})`);

room.rated = Math.min(p1NewElo, p2NewElo);

if (p1) p1.mmrCache[formatid] = +p1NewElo;
if (p2) p2.mmrCache[formatid] = +p2NewElo;

room.update();


const [data, error] = await ladderUpdatePromise;
let problem = false;

if (error) {
if (error.message === 'stream interrupt') {
room.add(`||Ladder updated, but score could not be retrieved.`);
} else {
room.add(`||Ladder (probably) updated, but score could not be retrieved (${error.message}).`);
}
problem = true;
} else if (!room.battle) {
Monitor.warn(`room expired before ladder update was received`);
problem = true;
} else if (!data) {
room.add(`|error|Unexpected response ${data} from ladder server.`);
Expand All @@ -108,37 +126,7 @@ export class LadderStore {
return [p1score, null, null];
}

let p1rating;
let p2rating;
try {
p1rating = data!.p1rating;
p2rating = data!.p2rating;

let oldelo = Math.round(p1rating.oldelo);
let elo = Math.round(p1rating.elo);
let act = (p1score > 0.9 ? `winning` : (p1score < 0.1 ? `losing` : `tying`));
let reasons = `${elo - oldelo} for ${act}`;
if (!reasons.startsWith('-')) reasons = '+' + reasons;
room.addRaw(Utils.html`${p1name}'s rating: ${oldelo} &rarr; <strong>${elo}</strong><br />(${reasons})`);
let minElo = elo;

oldelo = Math.round(p2rating.oldelo);
elo = Math.round(p2rating.elo);
act = (p1score > 0.9 || p1score < 0 ? `losing` : (p1score < 0.1 ? `winning` : `tying`));
reasons = `${elo - oldelo} for ${act}`;
if (!reasons.startsWith('-')) reasons = '+' + reasons;
room.addRaw(Utils.html`${p2name}'s rating: ${oldelo} &rarr; <strong>${elo}</strong><br />(${reasons})`);
if (elo < minElo) minElo = elo;
room.rated = minElo;

if (p1) p1.mmrCache[formatid] = +p1rating.elo;
if (p2) p2.mmrCache[formatid] = +p2rating.elo;
room.update();
} catch (e) {
room.addRaw(`There was an error calculating rating changes.`);
room.update();
}
return [p1score, p1rating, p2rating];
return [p1score, data!.p1rating, data!.p2rating];
}

/**
Expand All @@ -149,4 +137,37 @@ export class LadderStore {
static async visualizeAll(username: string) {
return [`<tr><td><strong>Please use the official client at play.pokemonshowdown.com</strong></td></tr>`];
}

/**
* Calculates Elo for quick display, matching the formula on loginserver
*/
// see lib/ntbb-ladder.lib.php in the pokemon-showdown-client repo for the login server implementation
// *intentionally* different from calculation in ladders-local, due to the high activity on the main server
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Wait, in hindsight I think the only difference is because of ladder decay, which isn't implemented here.

Is the only difference here the 1300 vs the 1350? Maybe we should merge them.

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That's not the only difference; the numbers for scaling when elo < 1200 are also different.
ladders-local:

if (score < 0.5) {
  K = 10 + (previousUserElo - 1000) * 40 / 200;
} else if (score > 0.5) {
  K = 90 - (previousUserElo - 1000) * 40 / 200;
}

ladders-remote:

if (score < 0.5) {
  K = 20 + (previousUserElo - 1000) * 30 / 100;
} else if (score > 0.5) {
  K = 80 - (previousUserElo - 1000) * 30 / 100;
}

ladders-remote uses 20/80 instead of 10/90, and multiplies by 30 instead of 40.

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Interesting! We probably want to investigate the formulas more, later. But that's probably a job for a different PR.

private calculateElo(previousUserElo: number, score: number, foeElo: number): number {
// The K factor determines how much your Elo changes when you win or
// lose games. Larger K means more change.
// In the "original" Elo, K is constant, but it's common for K to
// get smaller as your rating goes up
let K = 50;

// dynamic K-scaling (optional)
if (previousUserElo < 1100) {
if (score < 0.5) {
K = 20 + (previousUserElo - 1000) * 30 / 100;
} else if (score > 0.5) {
K = 80 - (previousUserElo - 1000) * 30 / 100;
}
} else if (previousUserElo > 1300) {
K = 40;
} else if (previousUserElo > 1600) {
K = 32;
}

// main Elo formula
const E = 1 / (1 + Math.pow(10, (foeElo - previousUserElo) / 400));

const newElo = previousUserElo + K * (score - E);

return Math.max(newElo, 1000);
}
}