Starcraft AI blog

Steamhammer’s tables are fuller than others, partly because Steamhammer records more information than most bots and partly because I put more effort into analyzing my own bot’s results. Even so, the game records contain far more information than is summarized here. I have many features in mind that I’d like to add to my analysis scripts.

Some bottom line findings: 1. My preparation for specific opponents was largely successful, as far as it went. All prepared openings had at least a fair win rate, and most were among the most successful openings Steamhammer discovered throughout the tournament. 2. Steamhammer’s gas steal skill had value against many opponents, even though my first analysis of the skill suggested that it might not. (I have known for a long time that my first analysis had missed the truth.) It was able to judge pretty accurately whether stealing gas was effective versus a given opponent, so it could exploit it when successful and reduce the cost of trying it when unsuccessful.

Steamhammer managed 3 wins with 2 different openings, but basically nothing worked despite trying the full range from 4 pool to hive rush. Stealing gas did not help, but the situation was desperate so Steamhammer tried it 10% of the time. An interesting number is the enemy scout timing: The scout probe arrived at the zerg base with more consistent timing (arriving in a narrower time window) than against any other opponent. Part of Stardust’s recipe is good scouting.

Steamhammer again desperately tried every tech and timing known to zerg, and this time found a little success with a few of them—a sunken build, a lurker build, and two 2-hatch zergling wave builds. PurpleWave largely stuck with 2 gates. Stealing gas barely delayed Protoss from taking gas, but Steamhammer still tried 10% of the time—if you’re losing almost all games, it doesn’t hurt.

BananaBrain was the first opponent weak enough that Steamhammer was able to find answers and did not feel a need to throw in the kitchen sink. 2 hatch muta builds were the most successful (and the best was one specialized for play against terran), but zergling builds and hydra builds were also OK. I love that the defiler rush won a game (it’s not at all a practical opening, but against a bot...). Unlike Stardust and PurpleWave, unpredictable BananaBrain played a variety of builds—for example, the appearance of an enemy cloaked unit at 3:26 in one game suggests a dark templar rush. The gas steal was successful and delayed protoss from taking gas for nearly an entire minute, so Steamhammer went with it frequently.

Steamhammer upset Dragon. The success of 5 hatcheries before spawning pool means that Dragon was not aggressive early, to its detriment—or that Steamhammer recognized any early aggression as a rush and reacted correctly. 3 hatchery mutalisk builds were also good. Even 3 hatchery lurker was not bad, though on the face it appears unsuited to counter Dragon’s play style. The gas steal was not successful in terms of win rate, but Steamhammer noticed that it delayed Dragon’s gas for a long time so it tried anyway. Fewer than half the attempts to steal gas ended with the extractor successfully made, though. The 37 minute game (here 37:21, officially 37:22) was Steamhammer’s longest game of the tournament, except for a couple games versus EggBot that went to the 60 minute limit and had to be adjudicated on points.

Steamhammer failed to recognize McRave’s build in 2/3 of games, though we know from yeterday’s post exactly what they were, and that they should not have been hard to understand. I put more effort into recognizing rushes and proxies that change the whole course of the game than into regular builds, and the result is that Steamhammer’s understanding and prediction are sometimes spectacularly unhelpful. The 8DroneGas build is actually a 9 pool which makes a second hatchery; it’s called that because it ends up with 8 drones while flooding zerglings (it’s not the Styx build, but related). 5 games had cloaked units; I think that means that McRave researched burrow, because it does use burrow and does not seem to ever make lurkers. Steamhammer was unable to steal gas in 10 attempts, so it gave up trying.

Steamhammer found a variety of overpool openings to be best. Overpool is flexible; those openings play out quite differently. Microwave didn’t play 5 pool often because it didn’t work: Steamhammer’s rush recognition is improved this year, and it reacted well. The burrow openings and 8-8 dawn hydra rush are not appropriate for ZvZ; those choices could be improved. Unlike McRave, Microwave did not use burrow. Stealing gas failed, so Steamhammer gave it up quickly.

DaQin upset Steamhammer badly, and zerg fell back on exploring widely. One ling bust and a few macro builds were able to save some games against DaQin’s consistent forge expand (which Steamhammer often misrecognized as Turtle because it did not actively look for the expansion nexus). The gas steal is measured to increase the overall win rate from 18% to 22%, not bad.

ZZZKBot switches between its famous 4 pool (recognized as Fast rush; see the 100% win rate when the strategy was recognized) and a build with sunkens, two hatcheries, and 6 sudden mutalisks (recognized as Turtle). It seems that part of Steamhammer’s difficulty with ZZZKBot (I consider a 75% win rate to be low in this case) is due to poor scouting: See the rate of Unknown enemy strategies. A bigger part of it may be a problem with the exploration policy. ZvZ_OverpoolTurtle scored 97% and was discovered early, but was played in only 59 games out of 150.

Steamhammer does not use enemy scout timing as a clue to the enemy strategy, and it should. When a scout appears at your base in 39 seconds it must have been sent almost immediately. Either the enemy is rushing, or is terrified that you might. A comparison of past scout timings versus recognized strategies for this opponent could be strong evidence.

ZZZKBot takes gas only in its muta strategy, and then it has sunkens so that a gas steal cannot succeed. Steamhammer figured that out fairly quickly.

Steamhammer recorded only 149 games against UAlbertaBot, because it crashed one game, its only crash in the tournament. Against every other opponent, Steamhammer recorded all 150 games.

There was no need to test the gas steal. If you’re winning nearly all games, spending a drone to vary your play is not likely to gain anything. Another point is that UAlbertaBot often takes gas quite late, so stealing gas early is unlikely to pay off.

WillyT was a tough opponent for Steamhammer. The choice of zerg builds does not seem strong. I have no idea how the guardian rush won 2 games out of 5.

Ecgberht is a tricky opponent. If it knew how to defeat fast lurker builds, it would score a lot higher against Steamhammer.

EggBot is a cannon bot. Its builds were recognized as Proxy for close cannons, Contain for cannons farther away from zerg bases, or Turtle for distant cannons. Steamhammer tried a variety of openings, discarding one as soon as it had lost a single game because there were others that still scored 100%. Steamhammer understood that EggBot never took gas, so gas steal would gain nothing.

This is not all of Steamhammer’s zerg openings! The tournament wasn’t long enough for it to try everything.