[Rd] Speed question: passing arguments vs environment

[Duncan Murdoch]

On 2025-12-02 7:41 a.m., Therneau, Terry M., Ph.D. via R-devel wrote:
> I have a complex likelihood function f() to maximize, with lots of arguments (some of which set up indexes for derivatives, for instance).
> When using something like optim(), one can pass these arguments through via its � arg, or could make the likelihood function f() live in the same environment as the main routine so they are found directly.    Is there any advantage of one versus the other wrt speed?    At the end of the day, f() may get called thousands of times in a Hamiltonian MCMC.
> 
> Since R does not replicate arguments that are used in a read-only fashion, one might expect little to no penalty for having them on the call chain, unless the bookkeeping for copy-on-write is itself time consuming.
> 

I think there wouldn't be a big difference in timing, but I'd guess 
there'd be a slight advantage to having them in the environment of the 
objective function.  I'd recommend testing both ways if you want to be sure.

Here are the differences that might matter:

  - putting them as arguments has the overhead of constructing the 
argument list each time, and if the args are used, the overhead of 
resolving promises.

  - putting them in the environment of the function means lookups will 
take two steps:  the evaluation frame followed by its parent, instead of 
succeeding in the first lookup.

I suspect the overhead of arguments is bigger, but it's probably not 
very big.

Duncan Murdoch