“Hi Rob,

When there is no ambient file there is usually an ambient cache created in memory. If you don’t have an ambient file each rtrace process will build its own cache. I’m guessing that each process spends most of the time building the cache with a first point and the subsequent calculations are very quick. Because getting the cache to saturation is the majority of the calculation time and each processor is doing this independently before really getting going on the points it won’t matter if you have 1 or 16 processors, the simulation will take the same amount of time.

To completely turn off the ambient cache use -aa 0. I expect you will see a
linear correlation between number of processes and simulation times, but the
sim times will be much much longer.

On a side note, I’m very jealous of your 16 core mac pro!

Andy”

So, there you have it. The thing to take away here is that one would almost certainly take advantage of ambient caching in normal practice, so of course this new feature of rtrace works great.