content: /*******************************************************************************
   * Copyright (c) 2010 Haifeng Li
   *   
   * 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 smile.validation;
  
  import smile.math.Math;
  
  /**
   * Root mean squared error.
   * 
   * @author Haifeng Li
   */
  public class RMSE implements RegressionMeasure {
  
      @Override
      public double measure(double[] truth, double[] prediction) {
          if (truth.length != prediction.length) {
              throw new IllegalArgumentException(String.format("The vector sizes don't match: %d != %d.", truth.length, prediction.length));
          }
  
          int n = truth.length;
          double rss = 0.0;
          for (int i = 0; i < n; i++) {
              rss += Math.sqr(truth[i] - prediction[i]);
          }
  
          return Math.sqrt(rss/n);
      }
  
      @Override
      public String toString() {
          return "RMSE";
      }
  }
  