Query expansion in Lucene (4.x)

I was reading a paper about Query Expansion ( http://search.fub.it/claudio/pdf/CSUR-2012.pdf) and it said: "For instance, Google Enterprise, MySQL and Lucene provide the user with an AQE facility that can be turned on or off." I searched through the Lucene 4.1.0 source code, which is what I have d

Getting a similarity score for an arbitrary pair of documents or a query and a document

Is there an api in Lucene for finding the similarity score for two documents that have been randomly pulled from an index? What about for a query and a randomly selected document? I realize this isn't the standard purpose of Lucene, but I was given a task to compare similarity scores for the Simil

Setting Similarity classes in Benchmark .alg scripts

I'd like to compare the relevance scores that are returned when using the Similarity classes that are available in Lucene 4.x, and it seems like using the Benchmark component would be a good way to do that. It looks like the isn't currently a way to specify a Similarity class to use in the config s