docs: public static double logpdf(double x, double k, double lambda, double theta) {
      if(x <= theta || x == Double.POSITIVE_INFINITY) {
        return Double.NEGATIVE_INFINITY;
      }
      double xl = (x - theta) / lambda;
      return FastMath.log(k / lambda) + (k - 1) * FastMath.log(xl) - FastMath.pow(xl, k);
    }