public InverseGamma(double alpha, double beta) throws ParameterException {
		if (alpha <= 0 || beta <= 0) {
			throw new ParameterException("InverseGamma parameters alpha > 0, beta > 0.");
		} else {
			this.alpha = alpha;
			this.beta = beta;
			gamma = new Gamma(alpha, beta);
		}
	}