The CoG 2021 website is updated today with “accept joining PurpleWave,” though the Result page is updated only with a note, not in the picture showing the list of entrants. As expected, PurpleWave is officially in, and now they say so. Good!
Those who saw today’s stream of the second half of the SSCAIT round of 16 in the elimination bracket may be wondering why Steamhammer played the same losing opening three times in a row against PurpleWave. It’s easy to explain.
Before the tournament, PurpleWave was playing forge expand game after game against Steamhammer. Steamhammer experimented and found that it could win with 9 gas 9 pool, which is a strong ZvZ one-hatch mutalisk build. It is not a strong ZvP build, but before the tournament, the fast mutas scored 13-0 against the fast expands, not a single loss. PurpleWave was not ready to defend against air.
In the round robin phase, PurpleWave again opened the first game with forge expand, and lost to the one-hatch mutas. The score was 14-0. But PurpleWave had been updated for the tournament, and forgot whatever bug or other fixation had caused it to stick to the same strategy. In the second game, protoss varied, and the score went to 14-1. PurpleWave is ranked higher than Steamhammer and usually wins. 14-1 was statistically far and away the best available opening, so Steamhammer stuck with it. It saw during play that it had gotten into trouble and tried desperately to save itself, but the mischief came in the early opening and there was nothing for it; at best it could have lost more slowly.
An RPS analyzer that better predicts the enemy’s opening plan could have helped. Steamhammer would also have to pay more attention to the enemy’s predicted strategy; it deliberately ignores the prediction against long-familiar opponents. The only general way that I know for a bot to be sure that it’s time to switch plans is for it to model the game events and understand why it lost (“oh yeah, you can beat that every time”), which is much more powerful than comparing statistics. I hope to do that eventually, but it’s beyond the state of the art for now. Anyway, opening timing is first, and that feeds in too.
PurpleTickles of Dan Gant’s purple family is a bot that plays exclusively worker rush builds. It’s not highly ranked; it is #50 on BASIL, well below average. Steamhammer’s score against it is 29-1 on BASIL, and the rest of the BASIL top 10 have similar scores. But I thought this one Steamhammer-PurpleTickles game was fun and instructive.
Steamhammer’s counter to worker rush is spawning pool at 9 drones (sometimes less if drones are lost) followed by creep colony. The intention is that when the spawning pool finishes, the combination of zerglings and a morphing sunken colony will be insuperable. If the sunken completes, zerg is safe against almost any number of workers, so the opponent must prevent that at all costs.
Tickles selected a late worker rush this game, starting its attack when it had 8 probes. It left 1 probe mining and attacked with 7. The late rushes are more effective against Steamhammer, and I assume that Tickles has figured that out (it has won 1 game, after all). At the time of the picture, 1 further probe has been manufactured and is now crossing the map to join the attack.
Tickles does not have perfect worker micro, but it does know how to coordinate its probes so they attack together. Steamhammer has inferior worker micro, because each drone defends itself individually and the drones don’t work together. Its forces can be defeated “in detail,” as the military jargon goes. Also Steamhammer has sent a drone to scout, a questionable decision, so its mining workers barely outnumber the attackers. In general, when Tickles attacks the mineral line from one end, it is very successful in killing drones. When it approaches from a different direction, the probes do not coordinate as nicely and Steamhammer has less trouble. Tickles is not smart enough to figure out the right angle of attack, so the outcome of the battle can depend on the orientation of the mineral line relative to the base entrance.
The probes destroyed all mining drones with 5 surviving attackers (and 1 probe still mining at home). Steamhammer gave priority to zerglings, so 2 pairs of zerglings are about to hatch, but there is no money to morph the sunken. Vanquishing 4 zerglings with 5 probes is a tall order, but protoss is still mining and it’s definitely worth a try.
Well, the probes didn’t stand a chance, though it’s hard to tell with the overlord blocking the view. They held their ground and fought instead of trying to maneuver, a fatal mistake. Steamhammer’s scouting drone canceled its mission and returned immediately to mine, so zerg did not find the protoss base yet. The 4 victorious zerglings aimed for the wrong base at first, and also returned home to clear followup probes, but they were able to win by themselves after these little delays.
I see lessons in the game. 1. Coordinated micro is a key skill. PurpleTickles has it. 2. Steamhammer covered for its lack of that skill with a belt-and-suspenders strategy. It works. In games where the sunken starts to morph, PurpleTickles must stop it with the probes, but then mining continues and zerglings win anyway. One skill can often substitute for another. 3. When you have an advantage, try to fight head on, as Tickles did probe versus drone. A probe is a stronger fighting unit than a drone. When you have a disadvantage, go guerilla. Probes are not bad at fighting zerglings, but they have to avoid head-to-head combat, unlike Tickles. A probe can attack at will as long as it is taking only shield damage, then run away; protoss shields regenerate faster than zerglings heal. Use drills (the minerals are right there), or maneuver to separate one zergling and gang up on it. If the purple probe-versus-zergling micro were as superior as the probe-versus-drone micro, the probes might well have won.
I’m pretty sure it’s possible to defeat Steamhammer most of the time with a worker rush, though no bot has shown it yet. As in this game, gather your attacking workers at one end of Steamhammer’s mineral line and coordinate them to defeat the uncoordinated mining drones, sweeping down to the other end of the mineral line. I believe it can be done more efficiently than in this game, and if it’s quick enough then after wiping the drones there should be no minerals for zerglings, or to morph the sunken—Steamhammer tries to replace drones and doesn’t save up for future needs.
If some bot proves my theory, then I’ll have to update Steamhammer’s worker defense.
Steamhammer has played another good game against PurpleWave. This seems to happen regularly. See Steamhammer-PurpleWave games for a few older games (which are not as good as this one).
I don’t want to do the blow-by-blow for this game, but here’s a little of the story. 2 games ago, PurpleWave played its worker rush against Steamhammer and won. 1 game ago, Steamhammer countered the worker rush and, partly because the map was more favorable, held it off to win. PurpleWave’s worker attacks are coordinated and Steamhammer’s worker defense is not, so PurpleWave can often win even when Steamhammer plays an ideal counter build. Anyway, having lost, PurpleWave switched to its forge expand opening. Strategically, it’s the opposite of a worker rush.
Steamhammer continued to counter the opening of the previous game, and played its anti-worker rush build. It’s a cautious opening that expects cheese, and it goes so far as to make a sunken colony. It’s the opposite of how you want to play against a big economy build like forge expand. So, after an early fight where Steamhammer didn’t quite figure out how to exploit PurpleWave’s poor cannon placement, zerg was behind.
I want to make 2 points about the game. 1. Steamhammer’s ZvP is much improved. When PurpleWave moved out with its big army, zerg was still behind. Steamhammer put up a fierce fight and eventually wore down the attack and held, losing some drones but not enough to die. And zerg continued to play well after that. Earlier versions won the big fights only when PurpleWave overextended, which did not happen here—thank economy improvements. And earlier versions did not follow up as nicely after the big fight—thank tech improvements.
Point 2. Near the end of the game, Steamhammer expanded to a mined-out base. :-( This version was supposed to fix the last way that that could happen. There is a bug in choosing the base to expand to. I am walking the Path of Bugs and the path continues over the horizon.
“Somebody” voted in a bunch of Steamhammer versus PurpleWave games. PurpleWave played different openings. Past versions of PurpleWave dominated Steamhammer with the forge-expand opening, taking advantage of Steamhammer’s mistaken macro decisions and weak scouting and tendency to collapse tactically in a big fight. But this PurpleWave has been losing some; it has new weaknesses. So the games are not the best, but they are still interesting.
Some of the games were proxy 2 gates. There were wins and losses, but I found those games not as interesting.
This is the Steamhammer-PurpleWave game that Nepeta cast last Sunday, so I won’t go into detail. PurpleWave suffered bugs that caused it to warp buildings near the zerg forces and pull probes for no reason, so it did not develop its usual big advantage. What I find interesting about the game is the turning point, when zerg pulled decisively ahead: It was when protoss attacked the zerg natural and dealt great damage, destroying the drones.
The returning zerg army finally cleared the attack. The protoss army was trapped and could not retreat toward home. It should have “retreated” into the zerg main to try to deal more damage (and to pull the zerg army away from the front), but instead turned fatalistic and gave up without a fight. Meanwhile, zerg had many drones at other bases and quickly restored the losses, while the lost protoss army was not as easy to replace. The value of destroying drones depends not on the number of drones you kill, but on the number that survive somewhere....
This game was also a forge-expand, but the play was quite different. No obvious bugs bit. PurpleWave built 4 cannons, which is plenty for most circumstances... and Steamhammer busted them anyway.
Steamhammer killed probes too. Then I tore my hair out in frustration, because instead of pressing for the win, Steamhammer decided it was more important to simultaneously plant a spire, hatchery, evo chamber, and hydra den, and also grow its economy. Notice in the picture that, although Steamhammer has spent 4 drones on buildings, it is still ahead in workers—and PurpleWave has cautiously pulled probes for defense. The spire, by the way, was left unused until late. With 2 bases, PurpleWave eventually caught up from far behind and the game was on again.
Fortunes turned again, like last time, when PurpleWave overpressed and lost too much army at Steamhammer’s natural. Seconds after this picture, protoss went from ahead in army size to well behind. Zerg quickly replaced drone losses and soon broke into the protoss natural in return.
PurpleWave went 2 gate zealots into expansion. Neither bot had much understanding of the situation. Steamhammer massed lings, an all-in play to smash the opponent. In practice it’s successful against most bots, but zerg ends up way behind in economy. Protoss can play defensively for a while and then win easily—that’s how Tyr protoss beats Steamhammer.
The game is not long or exciting. PurpleWave expanded in the face of the zerg swarm and did not have enough zealots. I include it to show how little bots understand strategy. In the picture, Steamhammer has half the workers of protoss. With any insight into the army-economy balance, you have to conclude that it is not a time for protoss to take a risk like expanding or moving out. The zealots again went fatalistic; as soon as they realized that they had lost, they stopped fighting and (unable to retreat far) were caught and died. You can also see that in the picture. Steamhammer has related weaknesses that are different but as severe.
PurpleWave might have had a chance if it retreated to the ramp and canceled the nexus. It was the best option, at least.
I expect that PurpleWave will fix its bugs before long and start winning again.
Next: More games, versus McRave and KillAll.