RatioFunction.java

/*
 * Class:        RatioFunction
 * Description:  Represents a function computing a ratio of two values.
 * Environment:  Java
 * Software:     SSJ 
 * Copyright (C) 2001  Pierre L'Ecuyer and Universite de Montreal
 * Organization: DIRO, Universite de Montreal
 * @author       
 * @since
 *
 *
 * Licensed 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 umontreal.ssj.util;

public class RatioFunction implements MultivariateFunction {
   private double zeroOverZero = Double.NaN;

   public RatioFunction() {
   }

   public RatioFunction(double zeroOverZero) {
      this.zeroOverZero = zeroOverZero;
   }

   public double getZeroOverZeroValue() {
      return zeroOverZero;
   }

   public void setZeroOverZeroValue(double zeroOverZero) {
      this.zeroOverZero = zeroOverZero;
   }
 
   public int getDimension() {
      return 2;
   }
 
   public double evaluate(double... x) {
      if (x.length != 2)
         throw new IllegalArgumentException("Invalid length of x");
      if (x[0] == 0 && x[1] == 0)
         return zeroOverZero;
      return x[0] / x[1];
   }
 
   public double evaluateGradient(int i, double... x) {
      if (x.length != 2)
         throw new IllegalArgumentException("Invalid length of x");
      switch (i) {
      case 0:
         return 1.0 / x[1];
      case 1:
         return -x[0] / (x[1] * x[1]);
      default:
         throw new IndexOutOfBoundsException("Invalid value of i: " + i);
      }
   }
}