Eigen 3.4 release update

[zdebruine]

Thanks all for maintaining this fundamental resource for the R community!

Seeing that Eigen 3.4 is out, and it supports some very useful operations for matrix subsetting and reshaping, what is the plan for when these updates will be loaded into RcppEigen?

Thanks again!

[eddelbuettel]

Thanks for the heads-up, I don't follow Eigen that closely so I had missed the 3.4.0 release.

Updating RcppEigen is always a little bit manual because of CRAN demands. You can see past patches in the patches/ directory. I do not know if this will be harder or easier with 3.4.0, and I will have to find time to work on it. Maybe one evening next week ...

[zdebruine]

@eddelbuettel Thanks a lot for your efforts!

The new Armadillo-like matrix subsetting features are welcome additions!

[eddelbuettel]

@zdebruine It no longer builds once I pivot to 3.4.0. It blows up immedialy at the junction (very top of the patch file) where @dmbates once found a way to accomodate cholmod. Now I just either tells me 'cholmod.h' not found (if I leave it as is) or, if I reenable what worked with Eigen 3.3.*, an error from the templates.

I don't really use RcppEigen and I mostly played stand-in maintainer while e.g. @yixuan did some heavier lifting a while back to get it adjusted. I just don't have the time to dive into this for a code base that I don't use. Maybe between you, @bbolker, ... someone can muster the will and skill to update this. Otherwise it may remain at 3.3.9 for a while I am afraid.

[zdebruine]

If the PR submitted by @yixuan doesn't suffice, I'm happy to take a deeper look later this week.

[eddelbuettel]

We will see how it goes. It may also make sense to talk to the (r)stan folks.

[eddelbuettel]

See #123 -- help with RcppEigen towards Eigen 3.4.0 would be greatly appreciated.

[eddelbuettel]

We're there now -- see #103 and PR #102 -- and it is arriving on CRAN now.