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APM is not everything in StarCraft

by Ben Weber on 05/05/11 08:26:00 pm   Expert Blogs   Featured Blogs

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The following blog post, unless otherwise noted, was written by a member of Gamasutra’s community.
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One of the requirements of expert-level StarCraft: Brood War gameplay is the ability to execute commands rapidly. It is common for professional players to execute over 300 APM (actions per minute) during peak gameplay. Increasing APM is important for RTS players, because it can increase the effectiveness of units in battle. However, players that place too much emphasis on micromanagement may fall behind in other aspects of gameplay, such as economy.

Bots have the potential for a much higher APM than human players, because they can simultaneously send orders to units all over the map. But does the potential for unlimited APM give bots too much of an advantage over human players? This is a question that consistently came up in discussions surrounding the StarCraft AI Competition. The winner of the competition was UC Berkeley’s Overmind. The Overmind was able to defeat the other bots by exploiting mutalisks, which are flying units capable of simultaneously moving and attacking. During battles, it often performs over 10,000 APM.

One of the possible conclusions that can be made from the competition is that execution is more important than strategic decision making in StarCraft. Essentially, exploiting the nearly unlimited APM available to bots breaks the game and nullifies the need for strategy. I disagree with this conclusion, because I have been working on a bot (EISBot) that is able to frequently defeat the Overmind using approximately 200 APM. A match between EISBot and the Overmind is shown below (video).

EISBot (green) versus Overmind (green)
There are two main reasons why a bot with a lower APM can win matches against the Overmind. First, there is no dominant strategy in StarCraft and therefore there is a counter to every strategy. Second, it is possible that several of the orders issued have no impact on the outcome of the game.

EISBot currently uses a mostly fixed strategy and this strategy was not intended to be a counter to the Overmind’s build order. Therefore, the ability of EISBot to win against the Overmind is the result of effective action selection. Rather than constantly spamming orders repeatedly, EISBot attempts to perform actions only when necessary, such as commanding a unit to flee when its health is low. While the actual APM of EISBot is quite low, the effective APM of EISBot is large, because most actions are intentional.

A comparison of the APM of EISBot and the Overmind is shown in the chart below. Overall, EISBot has a much lower APM, averaging at 207 versus the Overmind’s 3,397. There are several peaks in the Overmind’s APM, resulting from waves of zerglings and mutalisks being micromanaged. The goal of micromanaging units is to increase the effectiveness of each unit. However, having too large of an APM reduces the effectiveness of units, because the average damage output of each unit is reduced.
APM of Overmind versus EISBot
While demonstrating high APM in StarCraft is impressive, a larger APM does not always equate to better performance. Therefore, based on this example, it appears that the APM of a bot does not need to be limited in order to level the playing field between humans and bots in StarCraft.

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