Game Development Reference
In-Depth Information
with less and less input data, because there is not enough time between decisions
to gather enough data. You may need to analyze the data from several cycles of
the decision loop to reliably discern any trends. In this case, you also need to
determine the minimum number of data points required.
The stock market illustrates this dilemma quite well. Trades can be executed in
about a minute. But how long does it take to reliably determine a trend? For a
day-trader, five minutes may suffice. For a buy-and-hold, fee-averse investor, the
answer may be one quarter or even one year. For the first investor, one hour is an
eternity, and for the second investor, one hour is insignificant.
To be effective, feedback loops need to take long enough that real trends can be
distinguished from noise. In the case of our software agents, our feedback loops
need to take enough time that the agents can meaningfully act in ways that will
cause interactions. Games do have an inherent upper limit on effective
feedback speed, which we will see shortly when we look at feedback in Cars and
Trucks .
Slow Feedback
Slow feedback loops give rise to plodding systems such as freight trains that often
travel for miles before appreciably changing their speed. Technically, the feed-
back part is fast, but the control part is slow. The train engineer can hit the air
brakes or the throttle very quickly, but the train needs time to change speed. For
our purposes, we are combining feedback and control for simplicity and because
software systems are far less constrained on the control side than physical systems
are. If the feedback loop for a flock of boids takes too long, a boid that is too close
to its flock mates will fly away from them long enough that it will no longer
regard them as flock mates. A boid that is correcting for excess separation may
collide with all the other flock mates that are making the same correction.
Slow feedback fights against the interaction needed for emergent behavior to
appear. An e-mail exchange would be too slow for use in most games. Instant
messaging provides far faster feedback and enables a sense of ''being there'' to
emerge. Face-to-face conversation provides feedback at a rate that encourages a
wide range of emergent behaviors.
Fast feedback loops give rise to frenetic systems such as mayflies, constantly
darting here and there at the slightest input; slow feedback gives us freight trains.
Neither would be satisfactory at controlling an automobile. The timing of the
feedback has to be appropriate to the situation. Our project gives a good example
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