stats_variance
  (PECL stats >= 1.0.0)
stats_variance — Returns the variance
  
 
 
  参数
  
   
    
     a 
     - 
      
       The array of data to find the standard deviation for. Note that all 
       values of the array will be cast to float.
      
      
    
    
     sample 
     - 
      
       Indicates if a represents a sample of the 
       population; defaults to false.
      
      
    
   
  
  
 
  返回值
  
   Returns the variance on success; false on failure.