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SSCAIT PurpleWave-Steamhammer game

Another interesting game was PurpleWave v Steamhammer.

PurpleWave opened with two gates on one base but noticed a lot of zerglings. It cautiously added cannons at its ramp before moving out to pressure. It was an overstep: The ramp with zealots was unassailable, but as it happened Steamhammer defeated the zealots in the field and then the cannons over the ramp in detail, before being chased out by new zealots. On the next moveout, zerglings again broke into the base, killed the new cannon, and did away with many probes. Zerg evened the worker count but could not quite pull a win. Stamhammer switched to droning up, and it was the start of a long fight. PurpleWave spent a lot of gas replacing observers.

A couple cannons are little defense if unsupported, and take away from the zealot count. The bigger issue is, how do you know when it’s safe to move out? The scouting probe was long dead, and sending a new probe does not necessarily reveal the zergling count. Speedlings could easily catch it before it gets far. For zerg, the eternal issue is the economy/army tradeoff. If Steamhammer had kept up zergling production, it would likely have won quickly because of the overconfident protoss play. But if PurpleWave held the ramp instead, zerg would have fallen behind and had no chance. Steamhammer is weak at managing the tradeoff in the middle game.

Starcraft. It’s a hard game.

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Dan on :

PW recognized 9 pool gas when it saw the Extractor go down. At that point it will shift into protection against Speedlings, which means continuing the 2-gate opener and adding cannons at the ramp.

The cannons are important against mass Speedling builds, even if they take away from Zealot production, because without extremely good ramp plugging the Speedlings will out-trade the Zealots you can make and break through. The limitation in the fights is surface area for attacking, and cannons give you a massive edge on that front. Even when they're more than necessary, PurpleWave aims to only employ them in games where Zerg is fairly all-in, like Steamhammer is in this game, and thus the investment doesn't reduce the economic inevitability of PurpleWave's win should it handle its business appropriately.

The big story in the game is that PurpleWave's Zealots are badly broken against Zerglings at the moment. Combine the following individually reasonable rules:

- Units don't target enemies they can't catch (because they're faster, and you're not ranged, and they're not already in range, and they're not attacking a base)

- If a unit is in a battle but has no valid targets, it doesn't want to fight

- If a squad's consensus is "don't fight", it retreats

This produces the dynamic you see where PW will move out with a reasonable number of Zealots, retreat rather than fight (which is sub-optimal but acceptable), but any Zealots that individually get engaged on will fight back and get picked off (which is what really endangers PW). Really PW needs a combat fairness modifier encouraging fights when far from home against a faster enemy.

The horrible broken-ness against Zerglings before Dragoons emerge causes many of PurpleWave's losses across the entire tournament: Both losses against ZZZKBot, and one loss each to Arrakhammer, Microwave, and CUNYBot (The other was a non-started game). This was a known weakness going into the tournament but not high priority given the likely composition of the elimination bracket.

I think PurpleWave's moveouts in this game would be correct if Zealots could fight half-decently. It's necessary if Zerg is droning, and overconfident against the ground truth but not bad enough to cede the advantage, If the Zealots fought rather than split up, they might all die but Zerg would be left with few Drones and not enough Zerglings to press the attack. The cannons and continued Zealot production at home would be enough to ensure survival and an eventual win off the large economic differential.

The other major PW bugs in this game are the Observer micro, as you note, and PW's failure to spend minerals on Zealots, which I expect is a bug in its economy simulator and is reproduced in other games where PW is producing a Templar-Zealot composition. There are also issues of indecisive targeting, causing PW to repeatedly back off from killing the mineral base.

If you guessed that PW's next project is a targeting overhaul, you would be correct.

Jay Scott on :

In a lot of situations, when losing in the open field it’s best to sacrifice some so the rest can escape. I don’t think any bot has that skill, and in any case it may not have been the best choice here.

But surely zealots versus zerglings should fight shoulder-to-shoulder when they can.

I think bots are systematically worse with melee units than ranged units. Certainly all the top protoss bots are, and most of the zergs.

Dan on :

Agreed re: AI strength with melee vs. ranged. Melee combat requires understanding collisions and space, which is expensive to do discretely and to approximate requires intuition that's not easily coded. This is especially true for BW where units in close quarters behave irregularly.

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