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outputVector.direction=0.0 4 The Reactive Paradigm
outputVector.magnitude=0.0
}
return outputVector;
}

At this point, it is easy to illustrate how a potential field can be used by a
behavior, runaway, for the robot with a single sensor. The runaway behav-
ior will use the repulsive() function as the motor schema, and a function
readSonar() as the perceptual schema. The output of the behavior is a
vector. runaway is called by the robot on every update cycle.

vector runaway( ){
double reading;
reading=readSonar();//perceptual schema
vector=repulsive (reading, MAX_DISTANCE); //motor schema
return Voutput;
}
while (robot==ON)
{
Vrunaway=runaway(reading); // motor schema
turn(Vrunaway.direction);
forward(Vrunaway.magnitude*MAX_VELOCITY);
}

4.4.5 Combination of fields and behaviors

As stated earlier in the chapter, the first attribute of a true potential fields
methodology is that it requires all behaviors to be implemented as potential
fields. The second attribute is that it combines behaviors not by one sub-
suming others, but by vector summation. A robot will generally have forces
acting on it from multiple behaviors, all acting concurrently. This section
provides two examples of how multiple behaviors arise and how they are
implemented and combined.
The first example is simple navigation, where a robot is heading for a goal
(specified as “10.3m in direction ”) and encounters an obstacle. The motor