Parallel autodiff v3

[wds15]

Ok… will run it after I change the nesting stuff as explained in the PR.

EDIT: Looks a bit odd for 2 cores, but other than that its cool:

speedup grainsize= 0

walltime grainsize = 0

speedup grainsize bigger

walltime grainsize bigger

Cool stuff!

[Bob_Carpenter]

@martinmodrak

So if you didn’t plan to do so already, please do start another thread once the dust settles, so that more people actually provide fedback on the proposal.

I hope this is heading toward a design document in our design-docs repo. Once there’s a concrete, self-contained proposal, then we can comment on the PR.