docs: private static double abramowitzStegunFormula26p5p22(final double a, final double b,
        final double yp) {
      final double b2m1 = (2.0 * b) - 1.0;
      final double a2m1 = (2.0 * a) - 1.0;
      final double lambda = ((yp * yp) - 3.0) / 6.0;
      final double htmp = (1.0 / a2m1) + (1.0 / b2m1);
      final double h = 2.0 / htmp;
      final double term1 = (yp * (Math.sqrt(h + lambda))) / h;
      final double term2 = (1.0 / b2m1) - (1.0 / a2m1);
      final double term3 = (lambda + (5.0 / 6.0)) - (2.0 / (3.0 * h));
      final double w = term1 - (term2 * term3);
      final double xp = a / (a + (b * (Math.exp(2.0 * w))));
      return xp;
    }