code: public static float viarance(float[] c) {
  		float aver = average(c);
  		float via = 0.0f;
  		for(int i=0;i<c.length;i++){
  			float diff = c[i]-aver;
  			via+=diff*diff;
  		}
  		return via/c.length;
  	}
docs: 计算方差
  @param c
  @return