[pymvpa] Pkg-ExpPsy-PyMVPA Digest, Vol 62, Issue 2

[Ricky Savjani]

Roberto,

Thanks very much, this answered my question perfectly! Also, thanks for the
links on the interpretation, that was also very helpful.

-Ricky


On Wed, Apr 3, 2013 at 7:00 AM, <
pkg-exppsy-pymvpa-request at lists.alioth.debian.org> wrote:

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>    1. Re: SVM weights - positive and negative values (Roberto Guidotti)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Tue, 2 Apr 2013 16:24:19 +0200
> From: Roberto Guidotti <robbenson18 at gmail.com>
> To: Development and support of PyMVPA
>         <pkg-exppsy-pymvpa at lists.alioth.debian.org>
> Subject: Re: [pymvpa] SVM weights - positive and negative values
> Message-ID:
>         <CAGj93cHSb3xuLsqa9B8=7kX179d8d1xHfgeEEYewg=_
> jkwCrNQ at mail.gmail.com>
> Content-Type: text/plain; charset="iso-8859-1"
>
> Dear Ricky,
>
> basically I look at classifier estimates attribute (clf.ca.estimates) and
> at predictions (clf.ca.predictions), since the prediction is based on svm
> decision function sign, you could derive the class label (predictions) from
> the decision function sign (estimates).
>
> For the interpretation you can look at a discussion on this forum, in which
> I asked about weights signifiance:
>
> http://lists.alioth.debian.org/pipermail/pkg-exppsy-pymvpa/2011q2/001752.html
>
> R
>
>
> On 31 March 2013 22:11, Ricky Savjani <rsavjani at gmail.com> wrote:
>
> > Hi PyMVPA team,
> >
> > I had a quick question (or perhaps just pt of confusion) on the output of
> > SVM weights using a sensitivity_analyzer. In particular, I think that the
> > sign (positive vs negative) of the svm weights reflects the weighting for
> > the particular target (say 'class1' vs "class2"). I think positive values
> > would be associated with class1 and negative values to be associated with
> > class2. But how can you be sure which target corresponds to positive
> values
> > in the SVM weights? Is it simply alphabetically, meaning class1 would
> take
> > on positive values and class2 negative values? Or is this entirely the
> > incorrect interpretation of the SVM weights that are output by the
> > sensitivity analyzer?
> >
> > Thanks very much for the help.
> >
> > -Ricky
> >
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