samoa-api/src/main/java/org/apache/samoa/moa/classifiers/core/splitcriteria/SDRSplitCriterion.java

package org.apache.samoa.moa.classifiers.core.splitcriteria;

/*
 * #%L
 * SAMOA
 * %%
 * Copyright (C) 2014 - 2015 Apache Software Foundation
 * %%
 * 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.
 * #L%
 */

public class SDRSplitCriterion extends VarianceReductionSplitCriterion {
  private static final long serialVersionUID = 1L;

  public static double computeSD(double[] dist) {
    int N = (int) dist[0];
    double sum = dist[1];
    double sumSq = dist[2];
    return Math.sqrt((sumSq - ((sum * sum) / N)) / N);
  }

}