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tomz / libsvm-ruby-swig

Ruby interface to LIBSVM (using SWIG)
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Bug in ruby Model class' predict_probability() method #3

Open dparis opened 12 years ago

dparis commented 12 years ago

At https://github.com/tomz/libsvm-ruby-swig/blob/master/libsvm-3.1/ruby/svm.rb#L280:

#only C_SVC,NU_SVC goes in
if not @probability
    raise TypeError, "model does not support probabiliy estimates"
end

You're assuming that @probability will be false if it's not set, but from what I can tell the valid values are integer 1 and 0. Ruby does not consider zero to evaluate to boolean false.

This was a pain to track down; my codebase had a bug where I thought probabilities had been enabled on the model, but it wasn't actually being set. Since the TypeError is never raised in that case, the probability values are returned as if everything is fine. However, since the underlying LibSVM model doesn't have valid probability values defined, the C code returns garbage unallocated data cast into floats as the probability values to ruby. This was deeply confusing as I initially didn't know that the data was unreasonable until I started working with the results more closely. :(

tomz commented 12 years ago

thanks dparis for finding this, looks like changing line 212 to the following will fix it?

@probability = (svm_check_probability_model(@model) == 1)

dparis commented 12 years ago

Yes, that should work.

While I've got your attention, is there any chance you could republish the most recent version to rubygems? The version on rubygems is still using LibSVM 2.9.

As well, I've also got some feature requests that should be fairly straightforward. If you are going to update the published gem, would you mind waiting until I can get a pull request to you with the new feature additions? They're mostly to expose a few more properties or methods through the Model interface, nothing critical but it would allow me to clean up my code a bit. I could even take a look at fixing #2 while I'm at it.

tomz commented 12 years ago

Ok sounds good, feel free to send your pull requests when you are ready. Looks like I've already upgraded the github version to LibSVM 3.1(I probably forgot to publish it), I think the latest is 3.1.1, I will get that in when I get a chance.

dparis commented 12 years ago

Excellent. I'll try to have those sent out in the next day or two, time permitting.

dparis commented 12 years ago

I haven't forgotten about this, just been extra busy this last week or so. I'm hoping to have some time late tonight and tomorrow to get around to this stuff.

Cheers!