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The Apache Commons Math project is a library of lightweight, self-contained mathematics and statistics components addressing the most common practical problems not immediately available in the Java programming language or commons-lang.

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/*
 * 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.math3.ode.sampling;

import org.apache.commons.math3.exception.MaxCountExceededException;


/**
 * This interface represents a handler that should be called after
 * each successful step.
 *
 * The ODE integrators compute the evolution of the state vector at
 * some grid points that depend on their own internal algorithm. Once
 * they have found a new grid point (possibly after having computed
 * several evaluation of the derivative at intermediate points), they
 * provide it to objects implementing this interface. These objects
 * typically either ignore the intermediate steps and wait for the
 * last one, store the points in an ephemeris, or forward them to
 * specialized processing or output methods.
 *
 * @see org.apache.commons.math3.ode.FirstOrderIntegrator
 * @see org.apache.commons.math3.ode.SecondOrderIntegrator
 * @see StepInterpolator
 * @since 1.2
 */

public interface StepHandler {

    /** Initialize step handler at the start of an ODE integration.
     * 
     * This method is called once at the start of the integration. It
     * may be used by the step handler to initialize some internal data
     * if needed.
     * 
     * @param t0 start value of the independent time variable
     * @param y0 array containing the start value of the state vector
     * @param t target time for the integration
     */
    void init(double t0, double[] y0, double t);

    /**
     * Handle the last accepted step
     * @param interpolator interpolator for the last accepted step. For
     * efficiency purposes, the various integrators reuse the same
     * object on each call, so if the instance wants to keep it across
     * all calls (for example to provide at the end of the integration a
     * continuous model valid throughout the integration range, as the
     * {@link org.apache.commons.math3.ode.ContinuousOutputModel
     * ContinuousOutputModel} class does), it should build a local copy
     * using the clone method of the interpolator and store this copy.
     * Keeping only a reference to the interpolator and reusing it will
     * result in unpredictable behavior (potentially crashing the application).
     * @param isLast true if the step is the last one
     * @exception MaxCountExceededException if the interpolator throws one because
     * the number of functions evaluations is exceeded
     */
    void handleStep(StepInterpolator interpolator, boolean isLast)
        throws MaxCountExceededException;

}