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