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A Java's Collaborative Filtering library to carry out experiments in research of Collaborative Filtering based Recommender Systems. The library has been designed from researchers to researchers.
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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;

import java.util.Collection;

import org.apache.commons.math3.analysis.solvers.UnivariateSolver;
import org.apache.commons.math3.ode.events.EventHandler;
import org.apache.commons.math3.ode.sampling.StepHandler;

/**
 * This interface defines the common parts shared by integrators
 * for first and second order differential equations.
 * @see FirstOrderIntegrator
 * @see SecondOrderIntegrator
 * @since 2.0
 */
public interface ODEIntegrator  {

    /** Get the name of the method.
     * @return name of the method
     */
    String getName();

    /** Add a step handler to this integrator.
     * The handler will be called by the integrator for each accepted
     * step.
     * @param handler handler for the accepted steps
     * @see #getStepHandlers()
     * @see #clearStepHandlers()
     * @since 2.0
     */
    void addStepHandler(StepHandler handler);

    /** Get all the step handlers that have been added to the integrator.
     * @return an unmodifiable collection of the added events handlers
     * @see #addStepHandler(StepHandler)
     * @see #clearStepHandlers()
     * @since 2.0
     */
    Collection getStepHandlers();

    /** Remove all the step handlers that have been added to the integrator.
     * @see #addStepHandler(StepHandler)
     * @see #getStepHandlers()
     * @since 2.0
     */
    void clearStepHandlers();

    /** Add an event handler to the integrator.
     * Uses a default {@link UnivariateSolver}
     * with an absolute accuracy equal to the given convergence threshold,
     * as root-finding algorithm to detect the state events.
     * @param handler event handler
     * @param maxCheckInterval maximal time interval between switching
     * function checks (this interval prevents missing sign changes in
     * case the integration steps becomes very large)
     * @param convergence convergence threshold in the event time search
     * @param maxIterationCount upper limit of the iteration count in
     * the event time search
     * @see #getEventHandlers()
     * @see #clearEventHandlers()
     */
    void addEventHandler(EventHandler handler, double maxCheckInterval,
                         double convergence, int maxIterationCount);

    /** Add an event handler to the integrator.
     * @param handler event handler
     * @param maxCheckInterval maximal time interval between switching
     * function checks (this interval prevents missing sign changes in
     * case the integration steps becomes very large)
     * @param convergence convergence threshold in the event time search
     * @param maxIterationCount upper limit of the iteration count in
     * the event time search
     * @param solver The root-finding algorithm to use to detect the state
     * events.
     * @see #getEventHandlers()
     * @see #clearEventHandlers()
     */
    void addEventHandler(EventHandler handler, double maxCheckInterval,
                         double convergence, int maxIterationCount,
                         UnivariateSolver solver);

    /** Get all the event handlers that have been added to the integrator.
     * @return an unmodifiable collection of the added events handlers
     * @see #addEventHandler(EventHandler, double, double, int)
     * @see #clearEventHandlers()
     */
    Collection getEventHandlers();

    /** Remove all the event handlers that have been added to the integrator.
     * @see #addEventHandler(EventHandler, double, double, int)
     * @see #getEventHandlers()
     */
    void clearEventHandlers();

    /** Get the current value of the step start time t_i.
     * This method can be called during integration (typically by
     * the object implementing the {@link FirstOrderDifferentialEquations
     * differential equations} problem) if the value of the current step that
     * is attempted is needed.
     * The result is undefined if the method is called outside of
     * calls to integrate.
     * @return current value of the step start time t_i
     */
    double getCurrentStepStart();

    /** Get the current signed value of the integration stepsize.
     * This method can be called during integration (typically by
     * the object implementing the {@link FirstOrderDifferentialEquations
     * differential equations} problem) if the signed value of the current stepsize
     * that is tried is needed.
     * The result is undefined if the method is called outside of
     * calls to integrate.
     * @return current signed value of the stepsize
     */
    double getCurrentSignedStepsize();

    /** Set the maximal number of differential equations function evaluations.
     * The purpose of this method is to avoid infinite loops which can occur
     * for example when stringent error constraints are set or when lots of
     * discrete events are triggered, thus leading to many rejected steps.
     * @param maxEvaluations maximal number of function evaluations (negative
     * values are silently converted to maximal integer value, thus representing
     * almost unlimited evaluations)
     */
    void setMaxEvaluations(int maxEvaluations);

    /** Get the maximal number of functions evaluations.
     * @return maximal number of functions evaluations
     */
    int getMaxEvaluations();

    /** Get the number of evaluations of the differential equations function.
     * 
     * The number of evaluations corresponds to the last call to the
     * integrate method. It is 0 if the method has not been called yet.
     * 
     * @return number of evaluations of the differential equations function
     */
    int getEvaluations();

}