/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.commons.math.distribution;

import org.apache.commons.math.MathException;

/**
 * Base interface for probability distributions.
 *
 * @version $Revision$ $Date$
 */
public interface Distribution {
	/**
	 * For a random variable X whose values are distributed according to this
	 * distribution, this method returns P(X &le; x). In other words, this
	 * method represents the (cumulative) distribution function, or CDF, for
	 * this distribution.
	 * 
	 * @param x
	 *            the value at which the distribution function is evaluated.
	 * @return the probability that a random variable with this distribution
	 *         takes a value less than or equal to <code>x</code>
	 * @throws MathException
	 *             if the cumulative probability can not be computed due to
	 *             convergence or other numerical errors.
	 */
	double cumulativeProbability(double x) throws MathException;

	/**
	 * For a random variable X whose values are distributed according to this
	 * distribution, this method returns P(x0 &le; X &le; x1).
	 * 
	 * @param x0
	 *            the (inclusive) lower bound
	 * @param x1
	 *            the (inclusive) upper bound
	 * @return the probability that a random variable with this distribution
	 *         will take a value between <code>x0</code> and <code>x1</code>,
	 *         including the endpoints
	 * @throws MathException
	 *             if the cumulative probability can not be computed due to
	 *             convergence or other numerical errors.
	 * @throws IllegalArgumentException
	 *             if <code>x0 > x1</code>
	 */
	double cumulativeProbability(double x0, double x1) throws MathException;
}
