/*
 * 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.ode;

import org.apache.commons.math.ode.events.EventHandler;
import org.apache.commons.math.ode.sampling.StepHandler;

/**
 * This interface represents a first order integrator for differential
 * equations.
 * 
 * <p>
 * The classes which are devoted to solve first order differential equations
 * should implement this interface. The problems which can be handled should
 * implement the {@link FirstOrderDifferentialEquations} interface.
 * </p>
 *
 * @see FirstOrderDifferentialEquations
 * @see StepHandler
 * @see EventHandler
 * @version $Revision$ $Date$
 * @since 1.2
 */

public interface FirstOrderIntegrator extends ODEIntegrator {

	/**
	 * Integrate the differential equations up to the given time.
	 * <p>
	 * This method solves an Initial Value Problem (IVP).
	 * </p>
	 * <p>
	 * Since this method stores some internal state variables made available in
	 * its public interface during integration
	 * ({@link #getCurrentSignedStepsize()}), it is <em>not</em> thread-safe.
	 * </p>
	 * 
	 * @param equations
	 *            differential equations to integrate
	 * @param t0
	 *            initial time
	 * @param y0
	 *            initial value of the state vector at t0
	 * @param t
	 *            target time for the integration (can be set to a value smaller
	 *            than <code>t0</code> for backward integration)
	 * @param y
	 *            placeholder where to put the state vector at each successful
	 *            step (and hence at the end of integration), can be the same
	 *            object as y0
	 * @return stop time, will be the same as target time if integration reached
	 *         its target, but may be different if some {@link EventHandler}
	 *         stops it at some point.
	 * @throws IntegratorException
	 *             if the integrator cannot perform integration
	 * @throws DerivativeException
	 *             this exception is propagated to the caller if the underlying
	 *             user function triggers one
	 */
	public double integrate(FirstOrderDifferentialEquations equations, double t0, double[] y0, double t, double[] y)
			throws DerivativeException, IntegratorException;

}
