als-statistics/lib/analyze/cdf/betacfNR.js

Modular JS statistics toolkit for Node.js and the browser: descriptive stats, correlations (Pearson/Spearman/Kendall), t-tests & ANOVA (Student/Welch), reliability (Cronbach’s alpha), regression (linear/logistic), clustering (DBSCAN/HDBSCAN), and table/co

export function betacfNR(x, a, b, {EPS,FPMIN}) {
   const MAXIT = 200;
   let qab = a + b;
   let qap = a + 1;
   let qam = a - 1; // используется только для инициализации, но оставим для ясности
   let c = 1.0;
   let d = 1.0 - (qab * x) / qap;
   if (Math.abs(d) < FPMIN) d = FPMIN;
   d = 1.0 / d;
   let h = d;

   for (let m = 1; m <= MAXIT; m++) {
      const m2 = 2 * m;
      // Even step
      let aa = m * (b - m) * x / ((a + m2 - 1) * (a + m2));
      d = 1.0 + aa * d;
      if (Math.abs(d) < FPMIN) d = FPMIN;
      c = 1.0 + aa / c;
      if (Math.abs(c) < FPMIN) c = FPMIN;
      d = 1.0 / d;
      h *= (d * c);

      // Odd step
      aa = - (a + m) * (qab + m) * x / ((a + m2) * (a + m2 + 1));
      d = 1.0 + aa * d;
      if (Math.abs(d) < FPMIN) d = FPMIN;
      c = 1.0 + aa / c;
      if (Math.abs(c) < FPMIN) c = FPMIN;
      d = 1.0 / d;
      let delta = d * c;
      h *= delta;
      if (Math.abs(delta - 1.0) < EPS) {
         break;
      }
   }
   return h;
}