Reduce code bottlenecks

[pierucci]

Bottlenecks significantly reduce the speed of iterative functions for heterogeneity and probabilistic analysis. They should be identified and improvements should be suggested.

[pierucci]

Compiling functions with compiler::enableJIT() actually slows down the code...

[pierucci]

Biggest bottleneck: do_() call in eval_matrix().

[MattWiener]

This was actually (partially) addressed in a recent update. Sped up the do_() call in eval_matrix by around 4x. Of course there is always more to do. It might be useful to reprofile the code.

[pierucci]

I agree, thanks a lot for that! Furthermore bc84686d7aa4734c555a754e55be703805370660 added another 2x time speedup by running check_matrix() only once on a 3-D array instead of repeating it over 2-D matrices.

I'll still keep this issue open though to track codes bottlenecks elsewhere in the code.

[pierucci]

I suspect we could gain time in split_along_dim().

[MattWiener]

partially addressed by pull request #140.