What was the source of randomness in the Alpha Zero vs Stockfish match? My understanding is that Alpha Zero's algorithm was fixed after the "learning" phase, so would it come up with the same move for every position? Was the variability in the match entirely due to a Stockfish setting, or did Alpha Zero also display an element of randomness in its move selection?
I've noticed AlphaZero played 1.d4 and 1.Nf3 in http://www.chessgames.com/perl/chess.pl?tid=91944&amp;crosstable=1. Possibilities:


Mutlithreading (any software engineer can tell you it's not deterministic)
Monte Carlo Tree Search (the algorithm draws random paths, so it can't be deterministic)


Please note while the model's parameters are "fixed" (your own words), the actual move might be different. We don't have the source code for AlphaZero, but multithreading and MCTS are likely two major casues.