public static double logNormalPDF(double mu, double sigma, double x) {
		if (sigma < 0) throw new IllegalArgumentException("The parameter sigma, " + sigma + ", must be greater than or equal to zero");
		if (x < 0) {
			return 0.0D;
		} else {
			return Math.exp(-0.5D * Fmath.square((Math.log(x) - mu) / sigma)) / (x * sigma * Math.sqrt(2.0D * Math.PI));
		}
	}