/*
    * 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.math4.legacy.ode.nonstiff;
  
  import org.apache.commons.math4.legacy.ode.FirstOrderDifferentialEquations;
  import org.apache.commons.math4.legacy.ode.events.EventHandler;
  
  
  public class StepProblem
    implements FirstOrderDifferentialEquations, EventHandler {
  
    public StepProblem(double rateBefore, double rateAfter,
                       double switchTime) {
      this.rateAfter  = rateAfter;
      this.switchTime = switchTime;
      setRate(rateBefore);
    }
  
    @Override
  public void computeDerivatives(double t, double[] y, double[] yDot) {
      yDot[0] = rate;
    }
  
    @Override
  public int getDimension() {
      return 1;
    }
  
    public void setRate(double rate) {
      this.rate = rate;
    }
  
    @Override
  public void init(double t0, double[] y0, double t) {
    }
  
    @Override
  public Action eventOccurred(double t, double[] y, boolean increasing) {
      setRate(rateAfter);
      return Action.RESET_DERIVATIVES;
    }
  
    @Override
  public double g(double t, double[] y) {
      return t - switchTime;
    }
  
    @Override
  public void resetState(double t, double[] y) {
    }
  
    private double rate;
    private double rateAfter;
    private double switchTime;
  }