2012/8/22 Andreas Mueller <[email protected]>:
> Hi everybody.
> Recently I tried to hack at the SVM implementation, motivated by Lars' issue
> #918.
> While trying to figure out how to add support for callable kernels, I found
> out
> that precomputed kernels are not supported at all in the sparse svm, even
> though they are documented and look like they are tested.
>
> Trying to implement sparse kernels, I ran in a dead end somewhere in the C
> code
> (see my PR).
>
> Do you think we should try to fix that? Or should we warn / disable this
> "feature"
> which gives arbitrary results and randomly segfaults?
>
> The use-case that Lars was interested in doesn't actually need the sparse
> SVM,
> and I don't really see many applications for having a sparse matrix as a
> kernel.
> I guess we should rather change the checks such that callable kernels can
> take
> sparse input but have to produce dense kernel matrices.
>
> What do you think?

+1 for raising an exception for when the precomputed kernel matrix is
spares +  documenting it in the docstring.

+1 for opening a github issue / PR for adding support for sparse
precomputed kernel matrix later in the unlikely event of a user
encountering that use case "in real life".

-- 
Olivier
http://twitter.com/ogrisel - http://github.com/ogrisel

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