Merge learning to rank branch

[Richard Boulton]

We should work on merging the letor branch to trunk, to ensure it doesn't bitrot and get lost.

To get an overview of changes on the letor branch, see ​https://github.com/xapian/xapian/compare/master...svn%2Fgsoc2011-parth

Several things need to be done. Initially, by parth:

• add the letor/dir_contents file, so the build system works.

• remove letor/svm.h; the installed svm.h should be used instead.

• add the formulae to the docs/letor.rst file (in latex form, we can worry about making them display nicely later).

• add a description of which versions of libsvm should work to the docs/letor.rst file.

• remove the include of letor.h from xapian.h, and add a comment to the top of letor.h to indicate that it is not part of the official stable API.

At this point, parth can submit his code to google, and the gsoc project is finished.

Then, by olly or me:

• merge recent changes in trunk to the branch

• add detection of libsvm.h to configure.ac

• make the build skip letor if svm.h isn't available

• anything else required to merge the branch to trunk

• check that at least one buildbot is building the letor code.

I've marked this as milestone 1.3.0 so it doesn't get forgotten, but consider that a soft milestone.

[James Aylett]

What's the minimum version of libsvm required? 2.91 is in Ubuntu 11.04, but it's not the latest by any means. (Even assuming it's the same libsvm.) 2.85 is in Debian oldstable, and I've put it on atreus, but I suspect that's way out of date…

[parth]

Replying to james:

What's the minimum version of libsvm required? 2.91 is in Ubuntu 11.04, but it's not the latest by any means. (Even assuming it's the same libsvm.) 2.85 is in Debian oldstable, and I've put it on atreus, but I suspect that's way out of date…

libsvm-3.1 was used during the development of the Letor Project. By the way, my system works fine with system installed libsvm-3.0-2 too.

Parth.

[Richard Boulton]

The version of libsvm to use should be noted in the docs/letor.rst file.