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Locutus has a pylon harassment feature

Bot authors do a lot of creative stuff. Sometimes they are so creative that I can’t figure out the idea. Like this game between Locutus and Iron: Why did Locutus’s scout probe build pylons all over Iron’s territory?

too many pylons in the wrong place

It’s not a bug. It’s an intentional feature in this version of Locutus—here is the commit. It’s called “pylon harassment” and in this version it is hardcoded to happen only against Iron. A comment says:

    // We want to build a pylon. Do so when:
    // - We have enough resources
    // - We are not close to the enemy mineral line
    // - We are in sight range of an enemy building
    // - Nothing is in the way

“In sight range of an enemy building.” The pylons are meant to be seen. The intention must be to direct the opponent’s attention, to somehow divert it from doing something Locutus doesn’t want it to do, such as leave its base and attack Locutus.

In this game, Iron was not diverted at all, and won easily since Locutus had wasted a ton of minerals on pylons. I can imagine that some bots would go wrong. Those that pull workers to defend against proxy buildings might pull too many workers and stop mining, for example. Still, if your bot does make a mistake like that, it shouldn’t be hard to fix. So if pylon harassment is useful at all, I guess it must be a trick to easily defeat some weaker bots, or bots which make a certain class of blunder and are not being updated. Or possibly it is an unfinished feature, and the way it worked in this game is not how it is intended to work. I like the second theory better.

Another comment says

    // In the future, recognize how opponents react to pylon harass and store it in the opponent model

So in its final state, it is not intended to be hand-configured, but automatically selected. It could use code similar to the auto gas steal code already in Steamhammer, which decides whether to steal gas. Or it might use code similar to the plan recognizer to decide whether the opponent made a sensible or a silly reaction, and repeat if the opponent was silly.

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PurpleWaveDan on :

Iron has had this reaction to cannon rushes dating back to at least AIIDE 2016, in which it attacks the worker with three SCVs in reaction to a proxy pylon (AIUR and Trancik, the only cannon rushers at the time, both lose all their workers to this). It even calls the adorably-named function "makeSoldierForever" -- congrats, SCV, you're a soldier now! Kind of amusing, because that makes the Pylon attack an exploit of an exploit. Incidentally PurpleWave would probably also pull too many Probes vs. this and lose. Proxy reactions are hard.

Bruce on :

Take a look at any of the recent games of Locutus vs. Iron where Locutus wins to see how it’s intended to work. The basic idea is to exploit one of two reactions: either the opponent goes too aggressive and pulls a lot of workers to kill the pylon, or the opponent ignores the pylon, in which case they can be used to block mining, buildings, addons, etc. Iron overreacts, pulling two workers to chase the probe and 3-4 workers to kill the pylon, and then attacks the enemy main with 4-5 workers, so it ends up way behind economically. When I’m in a cheesy mood again, I’ll get around to testing some other bots and adding other behaviours.

Jay Scott on :

Hmm. Steamhammer pulls 2 workers for each proxy building, a decision made by Dave Churchill which I have never felt a need to change. If it is terran, it may pull one more SCV to chase the enemy scout. It’s simple, and so far it has worked well against proxies.

Dan on :

It is really quite tricky. I think in general attacking pylons with workers is a mistake. You lose money by doing it (100 minerals and time-discounted value of money, vs. way more than 100 minerals of mining time), and pylons by themselves don't do anything (one of the few exceptions being manner pylons, which even then should only be attacked by the trapped workers). The potential gotcha is ignoring the pylon, and then suddenly from the fog of war a cannon appears. Hard problems.

Jay Scott on :

It should be possible to get every worker out of the manner pylon trap (though I doubt any bot does). It seems clear to me that sometimes workers should attack the pylon. Consider the case where the manner pylon is about to fall: Then a worker might have the choice of running around behind the minerals to mine, or helping to kill the pylon and return mining to normal a little earlier. I imagine that perfect play depends on the entire situation.

Jay Scott on :

The pylon might even be for a forward shield battery for a zealot rush. That would be fun to implement. There are so many tricks that bots don’t try yet....

Jay Scott on :

Did you consider manner pylon? It’s not as easy to do, but it is objectively good and used in pro play. And bots don’t know how to react correctly, so....

Simon Prins on :

This was discussed on the Discord channel a while back.
Consider this replay: http://www.openbw.com/replay-viewer/?rep=https%3A%2F%2Fsscaitournament.com%2FReplays%2FLOCUTUS%2F262936-Locu_Iron-PvT.rep

Locutus builds a single pylon in Iron's base. Iron pulls a lot of workers, some to attack the pylon, some to attack the probe, but also a lot are sent straight to the opponents main. After the pylon is built, Iron only has about 6 svcs mining minerals and gas out of 15 total.

Iron is presumably a reacting to a perceived cannon rush. Note that a lot of the Cannon rush bots (AIUR, Jakub Trancik) have very bad worker defense, so in a way Iron is trying to do a trick to easily defeat some weaker bots himself.

Jay Scott on :

So both my theories were right: It was a blunder-exploiting trick, and it didn’t work as intended this game. Heh.

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