[amibroker] How to add "Alpha" to an exploration column?

["personal592002" <personal592002@xxxxxxxxx>]

How to add "Alpha" to an exploration column?  "Alpha" as defined buy
this entry in the AFL library. 

http://www.amibroker.com/library/detail.php?id=157&hilite=Correlation

For this exploration how do I get the last line working?

Filter = 1; 

AddColumn(Close,"Close",1.2);
AddColumn(Volume,"Volume",1.0);
AddColumn( ROC( Close, 15 ), "ROC(15)", 1.1 );
AddColumn(C/HHV( High, 240 ), "% 52 week high", 1.2); 
AddColumn(StochK(5,1), "5 Day Position",1.1);
//AddColumn(Alpha(C,240)"Alpha", 1.2);