I'm refering mostly to this paper here: http://clgiles.ist.psu.edu/papers/UMD-CS-TR-3617.what.size.neural.net.to.use.pdf
Current Setup:
I'm currently trying to port the neural-genetic AI solution that I have laying around to get into a multi-purpose multi-agent tool. So, for example, it should work as an AI in a game engine for moving around entities and let 'em shoot and destroy the enemy (so e.g. 4 inputs like distance x,y and angle x,y and 2 outputs like accelerate left,right).
The state so far is that I'm using the same amount of genomes as there are agents to determine the fittest agents. 20% of the fittest agents are combined with each other (zz, zw genomes selected) and create 2 babies for the new population each. The rest of the new population per-new-generation is selected randomly across the old population, including the fittest with-an-unfit-genome.
That works pretty well to prime the AI, after generation 50-100 it is pretty much human-unbeatable in a Breakout clone and a little Tank game where you can shoot and move around.
As I had the idea to use on evolution population for each "type of Agent" the question is now if it is possible to determine the amount of hidden layers and the amount of neurons in the hidden layers generically.
My setup for the tank game is 4 inputs, 3 outputs and 1 hidden layer with 12 neurons that worked the best (around 50 generations to be really strong).
My setup for a breakout game is 6 inputs, 2 outputs and 2 hidden layers with 12 neurons that seems to work best.
Done Research:
So, back to the paper: On page 32 you can see that it seems that more neurons per hidden layer need of course more time for priming, but the more neurons are in between, the more are the chances to get into the function without noise.
I currently prime my AI only using the fitness increase on successfully being better than the last try.
So in a tank game it means he successfully shot the other tank (wounded him 4 times is better, then enemy is dead) and won the round.
In the breakout game it's similar as I have a paddle that the AI can move around and it can collect points. "Getting shot" or negative treatment here is that it forgot to catch the ball. So potential noise input would be 2 output values (move-left, move-right) that depend on 4 input values (ball x, y, degx, degy).
Questions:
So, what kind of calculation for the amount of hidden layers and amount of neurons do you think can be a good tradeoff to have no noise that kills the genome evolution?
What is the minimum amount of agents until you can say that "it evolves further"? My current training setup is always around having 50 agents that learn in parallel (so they basically simulate 50 games in parallel "behind the scenes").
In sum, for most problems, one could probably get decent performance (even without a second optimization step) by setting the hidden layer configuration using just two rules: (i) number of hidden layers equals one; and (ii) the number of neurons in that layer is the mean of the neurons in the input and output layers.
-doug
In short. It's an ongoing area of research. Most (All that I know of) ANN using numerous neurons and H-Layers don't set a static number of either, instead they use algorithms to continuously modify these values. Usually constructing and destroying when outputs converge/diverge.
Since it sounds like you're already using some evolutionary computing, consider looking into Andrew Turner's work on CGPANN, I remember it getting pretty decent improvements on benchmarks similar to your work.