Avoid dense fill-in during margianlization

[sunbingfeng]

Feature

Update the marginalizeLeaves function to avoid dense fill-in.

Motivation

marginalizeLeaves will add new marginalization factor, which may cause the pose graph to be more and more dense.

The original iSAM package provided a sparsification method based on Chow-liu tree, but the tree construction is very time consuming, especially when the >20 keys are involved.

So, I'm wondering if GTSAM will provide some alternative method to sparsify the pose graph.

Thanks!

Pitch

marginalizeLeaves will keep the pose graph sparse.

[dellaert]

No plans. Happy to consider a PR :-)