Inaccuracy in PSO example?

[mariosky]

There is an inaccuracy on the PSO example on the smin and smax parameters. When the parameters are used in the constructor, they are similar to pmin and pmax:

toolbox.register("particle", generate, size=2, pmin=-6, pmax=6, smin=-3, smax=3)

They seem to be a minimum and maximum speed range. But when a particle is updated, they seem to have a different meaning:

for i, speed in enumerate(part.speed):
        if abs(speed) < part.smin:
            part.speed[i] = math.copysign(part.smin, speed)
        elif abs(speed) > part.smax:
            part.speed[i] = math.copysign(part.smax, speed)

In this case, with smin having a negative value, the first conditional will never be true. I think the code has a different meaning: smin is the minimum absolute value of the speed regardless of direction. So, a particle could have a speed from 0.3 to 3 negative or positive. I think this more useful. The case above works because it is symmetric around zero. Maybe the parameter should be:

toolbox.register("particle", generate, size=2, pmin=-6, pmax=6, smin=0, smax=3)

I think if someone wants different smin it will not work:

toolbox.register("particle", generate, size=2, pmin=-6, pmax=6, smin=-1, smax=3)