求陣列方差演算法實現?

Java實現求方差演算法

import java.util.List;

/**

* @title: FangCha.java

* @project: ssc

* @package: ssc.com.yuce

* @author: Edy

* @date: Aug 21, 2012

* @description: 方差

* @version: V1.0

*/

public class FangCha {

/**

* 求陣列方差

* @param num

* @return

*/

public static double getFangCha(List num) {

double avg = 0.0;

double count = num.size();

for (int i = 0; i < num.size(); i++) {

avg = avg + num.get(i);

}

avg = avg / count;

return getFangCha(num, avg);

}

/**

* 求陣列方差

* @param num

* @param avg

* @return

*/

public static double getFangCha(List num, double avg) {

double count = num.size();

double ff = 0.0;

for (int i = 0; i < num.size(); i ++) {

ff = ff + (num.get(i) - avg) * (num.get(i) - avg);

}

ff = ff / count;

return ff;

}

/**

* 求數列平均值

* @param list

* @return

*/

public static double getAverage(List list) {

double sum = 0;

int len = list.size();

for (int i = 0; i < len; i++) {

sum += list.get(i);

}

return sum / len;

}

/**

* 求陣列標準差

* @param list

* @return

*/

public static double getBZCha(List list) {

return Math.sqrt(getFangCha(list));

}

}