split the logllikelihood and its gradient

[zhou13]

See Issues #8.

[zhou13]

Not sure why the checks failed. It seems not related to the tests. It should pass all the nosetests.

[rmcgibbo]

Okay, I fixed the travis issues in #10, so if you rebase this PR on the current master, the tests should run.

[zhou13]

I rebased my branch and did a git push --force but it seems that the problem is still there. Could you have a check?

[rmcgibbo]

Is there a way that you can make it backwards compatible with the old API? Maybe using the same pattern that the jac argument to scipy.optimize.minimize uses, taking a callable or True? The reason is that for some of my applications, the gradient and objective have so many terms in common that once you've computed the objective, the gradient is basically free (and visa versa), so computing them from the same callback is more efficient than having two separate callbacks.

[rmcgibbo]

I rebased my branch and did a git push --force but it seems that the problem is still there. Could you have a check?

Hopefully fixed by #11.

[zhou13]

Is there a way that you can make it backwards compatible with the old API? Maybe using the same pattern that the jac argument to scipy.optimize.minimize uses, taking a callable or True.

That's a good idea. I will implement that.