docs: public static double pdf(double val, double shape, double location, double scale) {
      if(val < location) {
        return 0;
      }
      val = (val - location) / scale;
      double f = shape / scale * FastMath.pow(val, shape - 1.);
      if(f == Double.POSITIVE_INFINITY) {
        return 0;
      }
      double d = 1. + FastMath.pow(val, shape);
      return f / (d * d);
    }