docs: public static double logpdf(double x, double mu, double sigma) {
      if(x <= 0.) {
        return Double.NEGATIVE_INFINITY;
      }
      final double xrel = (FastMath.log(x) - mu) / sigma;
      return MathUtil.LOG_ONE_BY_SQRTTWOPI - FastMath.log(sigma * x) - .5 * xrel * xrel;
    }