Starcraft AI blog

There’s a striking pattern in the SSCAIT round of 8 that I want to point out. First, the video and the Liquipedia page. I’ll discuss the results. The round was made up of 6 newer and frequently updated bots, which were all paired against each other, and 2 old hands which were paired together. Each pair played a best of 5 match.

The old hands were Killerbot and XIMP, not updated for this tournament. They played a balanced match which was decided by strategy and tactics and fine details of play which the bots didn’t take into account. There weren’t any obvious or decisive bugs, it was about good everyday play.

Taking the rest of the matches from the top, Iron-Microwave went to Microwave because the zerg bot was able to break the terran wall. Iron knew how to repair its wall and made marines to defend it. But the marines were afraid of the zerglings which could not attack them through the wall, and did not shoot. I suppose that the combat simulator doesn’t understand the wall and says “uh oh, we’ll lose if the melee units get close, keep a safe distance!” Microwave won by exploiting a bug in Iron.

Steamhammer swept Arrakhammer 3-0 with 3 zergling builds in a row. Nepeta didn’t point it out in the video, but in each game Arrakhammer’s own zerglings fought piecemeal, inefficiently engaging with a partial force and then retreating, suffering more damage than they dealt. Steamhammer won by exploiting a bug in Arrakhammer.

CherryPi beat McRave 3-2 in a close match. McRave showed strategy weaknesses which deserve some of the blame. Nepeta’s points in the video are valid: Expand earlier, get +1 attack for the zealots to counter zerglings (since with +1 a zealot kills an unupgraded zergling in 2 hits instead of 3, a giant difference), and don’t cower in your own base when you play an aggressive 2 gate opening (you should never be behind in units for long). But McRave’s biggest weakness was that its high templar usually did not cast psionic storm, and seemed happy to suicide themselves. CherryPi won by exploiting the bug. In one game that CherryPi lost, zerg did not build the macro hatcheries it needed to keep up its zergling-heavy unit mix, and CherryPi’s mineral bank grew into the thousands. McRave won that game by exploiting a bug in CherryPi.

Two conclusions are loud and clear. 1. 6 of the 8 participants that made it this far are frequently updated and fast evolving. Only 2 old timers could keep up. The hard work to make many improvements pays off. 2. The same frequent updates leave bots vulnerable to bugs. The old hands were solid (at least they looked solid this time), and the fast movers had fragile spots.

I’m not sure there are any lessons for bot authors, other than “hard work pays off” and “fix the worst problems first,” both of which we already knew. The pattern in the results was so striking that I couldn’t ignore it.

Next: Steamhammer 1.4 change list.