Corrected rank normal distribution

package.json

@@ -16,7 +16,7 @@
     "@actions/github": "^4.0.0",
     "@testing-library/dom": "^7.20.0",
     "@testing-library/jest-dom": "^5.11.0",
-    "axios": "^0.19.2",
+    "axios": "^0.21.1",
     "axios-mock-adapter": "^1.18.1",
     "css-to-object": "^1.1.0",
     "husky": "^4.2.5",
@@ -28,7 +28,8 @@
     "emoji-name-map": "^1.2.8",
     "github-username-regex": "^1.0.0",
     "prettier": "^2.1.2",
-    "word-wrap": "^1.2.3"
+    "word-wrap": "^1.2.3",
+    "mathjs": "^9.0.0"
   },
   "husky": {
     "hooks": {

src/calculateRank.js

@@ -1,19 +1,9 @@
-// https://stackoverflow.com/a/5263759/10629172
+const { erf } = require("mathjs");
+const invSqrt2 = 1 / Math.sqrt(2);
+// https://mathworld.wolfram.com/NormalDistribution.html
 function normalcdf(mean, sigma, to) {
-  var z = (to - mean) / Math.sqrt(2 * sigma * sigma);
-  var t = 1 / (1 + 0.3275911 * Math.abs(z));
-  var a1 = 0.254829592;
-  var a2 = -0.284496736;
-  var a3 = 1.421413741;
-  var a4 = -1.453152027;
-  var a5 = 1.061405429;
-  var erf =
-    1 - ((((a5 * t + a4) * t + a3) * t + a2) * t + a1) * t * Math.exp(-z * z);
-  var sign = 1;
-  if (z < 0) {
-    sign = -1;
-  }
-  return (1 / 2) * (1 + sign * erf);
+  const a = (invSqrt2 * (to - mean)) / sigma;
+  return (1 + erf(a)) / 2;
 }
 
 function calculateRank({
@@ -57,8 +47,8 @@ function calculateRank({
     issues * ISSUES_OFFSET +
     stargazers * STARS_OFFSET +
     prs * PRS_OFFSET +
-    followers * FOLLOWERS_OFFSET + 
-    totalRepos * REPO_OFFSET 
+    followers * FOLLOWERS_OFFSET +
+    totalRepos * REPO_OFFSET
   ) / 100;
 
   const normalizedScore = normalcdf(score, TOTAL_VALUES, ALL_OFFSETS) * 100;

tests/calculateRank.test.js

@@ -13,6 +13,6 @@ describe("Test calculateRank", () => {
         prs: 300,
         issues: 200,
       }),
-    ).toStrictEqual({ level: "A+", score: 49.16605417270399 });
+    ).toStrictEqual({ level: "A+", score: 49.16605835034125 });
   });
 });