docs: public static double pdf(double val, double dof) {
      if(val <= 0 || val == Double.POSITIVE_INFINITY) {
        return 0.0;
      }
      final double k = dof * .5;
      return FastMath.exp((dof - 1.0) * FastMath.log(val) + (1 - k) * MathUtil.LOG2 - GammaDistribution.logGamma(k) - val * val / 2.);
    }