Re: [eigen] New Levenberg Marquardt stuff

["Radu B. Rusu" <radu.b.rusu@xxxxxxxxx>]

Dear Sameer,

Is there a particular reason why you'd like to remove the current LM implementation that Eigen has from the library? We 
have been using it for a long time, and are quite happy with it. There might be other implementations which are better, 
but there are use cases where the number of dependencies has to be very low, and one of our applications fits perfectly 
in this scenario. Eigen has a proven track record of being cross compilable on all the architectures that I can think 
of, with excellent unit tests, documentation, and really a fantastic user support, while other libraries are/do not. I'm 
bowing my hat every time I have a chance to the Eigen team, as they are an inspiration for other open source movements 
such as ours.

I think we can all agree that what Eigen did in the past few years changed the game completely for us C++-ers, as they 
made us move away from that ugly C code that we were using in the past while dealing with matrix operations / 
decompositions. That being said, I'd be more happy to see more solvers available in Eigen, either as part of the core or 
maybe the Eigen maintainers/developers can start adding additional modules ("libraries") alongside the core that deal 
with non-linear LS solvers. If there is code in CERES that is generally purpose and fits in the Eigen paradigm, it would 
be great to have it included it there. Why not have "libeigen-core", "libeigen-nonlinear", etc if adding more to the 
existing Eigen library is a problem?

Generally speaking, I think the libraries with the best support win in the long run. Our group has contributed and 
co-developed G2O at Willow Garage with Freiburg University, and we have also made contributions to GTSAM recently. 
However, even though the code in these graph optimizers might be excellent, the user support is orders of magnitude 
poorer than Eigen's, and it's most likely going to stay this way. The main programmers are PhD students and they simply 
do not have the time to build such comprehensive software packages as the Eigen community did or spend time with user 
support -- though one could argue that would be good for their careers in the long run ;)

So +1 to keep the existing LM code, and potentially improve it and/or add additional similar solvers to perhaps an extra 
Eigen module if people feel that Eigen is "growing too big". (I disagree that it does.)

Cheers,
Radu.
--
http://openperception.org

On 12/07/2012 03:07 PM, Sameer Agarwal wrote:
> Dear  Christoph,
> I think that discussion about releasing ceres is best had elsewhere rather than the eigen mailinglist.
>
>         Have you considered punting on the LM library entirely?
>
>         Ceres is almost uniformly better than what's there now, is heavily battle
>         tested in production both large (Street View) and small (Android, in every
>         Nexus 4), is BSD licensed, uses Eigen internally, has extensive sparse
>         support.
>
>
>     Well, it might use Eigen internally, but ceres' interface dealing a lot with double-pointers is far away from the
>     clearity of Eigen ...
>
>         It's not clear that Eigen dev's time is best spent working on LM when Ceres
>         exists.
>
>     As mentioned already by others, Eigen's LM module existed way longer than Ceres, and there existed a bunch of LM
>     implementations before that.
>     Furthermore, I agree with opinions raised by others that including a generic non-linear LS solver into Eigen
>     might/should not be the goal of Eigen, which IMHO should basically be a *linear* algebra package.
>     As long as no further dependencies are introduced (neither for compiling nor for licensing), I don't mind if some
>     small extensions are added, though (clearly not the case for ceres having 2--5 more dependencies).
>
>
> Keir and I are arguing exactly that, please do not add more stuff into eigen which has nothing to do with linear
> algebra. We are not arguing for adding Ceres to eigen, but to remove nonlinear optimization code from eigen.
>
> Sameer
>
>
>
>
>
>
>
>     Christoph
>
>
>
>     --
>     ------------------------------__----------------
>     Dipl.-Inf. Christoph Hertzberg
>     Cartesium 0.049
>     Universität Bremen
>     Enrique-Schmidt-Straße 5
>     28359 Bremen
>
>     Tel: +49 (421) 218-64252 <tel:%2B49%20%28421%29%20218-64252>
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