my question about lucene

[强继朋]

lucene,
           I hava a problem i don't know how to do, it's about Score Formula of 
lucene.  In the package of lucene, it provide a method  in Class Similarity. My 
question : if i want to only use some factors of Formula, such as TF and IDF. 
And then i add some additional factors, in aim to construct a new formula, 
which aren't provided by Formula. Finally, i sort the score by the new formula, 
and get the search's result.  what should i do?  Thank you !
                                                                                
                                                                     Student 
:Qiang JIpeng
                                                                                
                                                                       
2011.11.09