[Xapian-devel] Regarding Letor

Parth Gupta pargup8 at gmail.com
Sat Mar 22 18:38:02 GMT 2014

Hi Mayank,

> 1. Is fcount meant to store the number of features in the featurevector.h?
> What is the need to keep it inside the feature vector. Will it not be same
> for all the feature vectors. And by default that must be 19.

Yes 'fcount' would be same for all the feature vectors. It belongs to
feature vector because it's the property of feature vector. Every static
reference to number 19 should be changed by a dynamic reference fv.fcount
or something and when provided with the training data it should be set
automatically from the highest index of feature seen in the data if the
user does not set it explicitly.

> 2. In svmranker.cc there is a data member called weights[]. Is it possible
> to get the weights from the learned model in libsvm. Actually I can't find
> any in letor_internal_refactored.cc. And shouldn't there be a data member
> as struct  *svm_model** which will point to the model learnt so that
> functions *load_model* and *save_model* don't need an extra argument.

The svmranker uses libsvm for the training. The model file does not store
the weight vector clearly rather the model files contain support
vectors(SV). So we use the model loading module accordingly. But you can
analyse the model files and extract the weight vector if the model file
allows. I vaguely remember it was not so obvious to interpret model files
at that time.


> Thanks
> Mayank
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