μ8

Simple unsupervised machine learning package using Go 1.18 generics.

User information

μ8 (mu8) uses a simple genetic algorithm implementation to optimize a objective function. It allows optimizing floating point numbers, integers and anything else that can implement the 3 method Gene interface

The genetic algorithm implementation is currently ~150 lines long and is contained in population.go. It consists of the following steps:

1. Natural selection. Best individual conserved (population champion)
2. Mate.
3. Mutate babies.
4. Rinse and repeat.

The file mu8.go contains Genome and Gene interface definitions. Users should implement Genome interface and use Gene implementations from genes package.

There is an Islands Model Genetic Algorithm (IMGA) implementation in islands.go using the Islands type that makes use of a parallel optimization algorithm to make use of multi-core machines.

μ8 examples

Basic usage example

Everything starts with the mu8.Genome type on the user side. We define a type that implements it using a helper type genes.ContrainedFloat from the genes package. All this genes type does is save us the trouble of writing our own mu8.Gene implementation.

type mygenome struct {
	genoma []genes.ConstrainedFloat
}

func (g *mygenome) GetGene(i int) mu8.Gene { return &g.genoma[i] }
func (g *mygenome) Len() int               { return len(g.genoma) }

// Simulate simply adds the genes. We'd expect the genes to reach the max values of the constraint.
func (g *mygenome) Simulate() (fitness float64) {
	for i := range g.genoma {
		fitness += g.genoma[i].Value()
	}
    // fitness must ALWAYS be greater than zero for succesful simulation.
	return math.Max(0, fitness/float64(g.Len()))
}

We're almost ready to optimize our implementation to maximize it's fitness, which would simply be the addition of all it's genes.

Let's write the function that initializes a blank-slate mygenome

func newGenome(n int) *mygenome {
	return &mygenome{genoma: make([]genes.ConstrainedFloat, n)}
}

The function above may be confusing... what is the constraint on the number? By default genes.ConstrainedFloat uses the range [0, 1].

const Nindividuals = 100
individuals := make([]*mygenome, Nindividuals)
for i := 0; i < Nindividuals; i++ {
	genome := newGenome(genomelen)
	// This spices up the initial population so fitnesses are not all zero.
	mu8.Mutate(genome, src, .1)
	individuals[i] = genome
}

pop := genetic.NewPopulation(individuals, rand.NewSource(1), func() *mygenome {
		return newGenome(3)
})

const Ngeneration = 100
ctx := context.Background()
for i := 0; i < Ngenerations; i++ {
		err := pop.Advance(ctx)
		if err != nil {
			panic(err.Error())
		}
		err = pop.Selection(0.5, 1)
		if err != nil {
			panic(err.Error())
		}
}
fmt.Printf("champ fitness=%.3f\n", pop.ChampionFitness())

The final fitness should be close to 1.0 if the algorithm did it's job. For the code see mu8_test.go

Rocket stage optimization example

See rocket for a demonstration on rocket stage optimization. Below is the output of said program

champHeight:117.967km
champHeight:136.748km
champHeight:140.633km
champHeight:141.873km
champHeight:141.873km
champHeight:141.873km
champHeight:142.883km
champHeight:143.292km
champHeight:143.292km
champHeight:143.292km
champHeight:143.292km
our champion: 
Stage 0: coast=281.2s, propMass=0.0kg, Δm=99.35kg/s, totalMass=200.0
Stage 1: coast=0.0s, propMass=1.6kg, Δm=0.01kg/s, totalMass=21.6

Gradient "ascent" example

src := rand.NewSource(1)
const (
	genomelen      = 6
	gradMultiplier = 10.0
	epochs         = 6
)
// Create new individual and mutate it randomly.
individual := newGenome(genomelen)
rng := rand.New(src)
for i := 0; i < genomelen; i++ {
	individual.GetGene(i).Mutate(rng)
}
// Prepare for gradient descent.
grads := make([]float64, genomelen)
ctx := context.Background()
// Champion will harbor our best individual.
champion := newGenome(genomelen)
for epoch := 0; epoch < epochs; epoch++ {
	// We calculate the gradients of the individual passing a nil
	// newIndividual callback since the GenomeGrad type we implemented
	// does not require blank-slate initialization.
	err := mu8.Gradient(ctx, grads, individual, nil)
	if err != nil {
		panic(err)
	}
	// Apply gradients.
	for i := 0; i < individual.Len(); i++ {
		gene := individual.GetGeneGrad(i)
		grad := grads[i]
		gene.SetValue(gene.Value() + grad*gradMultiplier)
	}
	mu8.CloneGrad(champion, individual)
	fmt.Printf("fitness=%f with grads=%f\n", individual.Simulate(ctx), grads)
}

Contributing

Contributions very welcome! I myself have no idea what I'm doing so I welcome issues on any matter :)

Pull requests also welcome but please submit an issue first on what you'd like to change. I promise I'll answer as fast as I can.

Please take a look at the TODO's in the project: Ctrl+F TODO

References

Inspired by CodeBullets amazing video on the subject.

Logo work

Gopher rendition by Juliette Whittingslow.
Gopher design authored by Renée French is licensed by the Creative Commons Attribution 3.0 licensed.