[xigoi]

> No. Floating number arithmetic is deterministic. You don't get different answers for the same operations on the same machine just because of limited precision. There are reasons why it can be difficult to make sure that floating point operations agree across machines, but that is more of a (very annoying and difficult to make consistent) configuration thing than determinism.

Float addition is not associative, so the result of x1 + x2 + x3 + x4 depends on which order you add them in. This matters when the sum is parallelized, as the structure of the individual add operations will depend on how many cores are available at any given time.