From 17fff124da527d4d5b036decbf78ee98acb3f39a Mon Sep 17 00:00:00 2001
From: Guillaume Simonneau <2980507+khezen@users.noreply.github.com>
Date: Sat, 6 Mar 2021 01:18:46 +0100
Subject: [PATCH] crossover: produces two children (#30)

---
 crosser.go            |  2 +-
 examplegnetic_test.go | 16 ++++++++++------
 genetic.go            | 25 ++++++++++++++-----------
 mock_test.go          |  9 +++++++--
 4 files changed, 32 insertions(+), 20 deletions(-)

diff --git a/crosser.go b/crosser.go
index dd94377..e6c6be1 100644
--- a/crosser.go
+++ b/crosser.go
@@ -2,5 +2,5 @@ package evoli
 
 // Crosser produces a new individual from two individuals. This operators provides convergence to a population.
 type Crosser interface {
-	Cross(individual1, individual2 Individual) (Individual, error)
+	Cross(parent1, parent2 Individual) (child1, child2 Individual, err error)
 }
diff --git a/examplegnetic_test.go b/examplegnetic_test.go
index 66abc18..1e61e37 100644
--- a/examplegnetic_test.go
+++ b/examplegnetic_test.go
@@ -49,13 +49,17 @@ func (m HMutater) Mutate(indiv evoli.Individual) (evoli.Individual, error) {
 type HCrosser struct {
 }
 
-func (h HCrosser) Cross(indiv1, indiv2 evoli.Individual) (evoli.Individual, error) {
-	fIndiv1, _ := indiv1.(*HIndividual)
-	fIndiv2, _ := indiv2.(*HIndividual)
+func (h HCrosser) Cross(parent1, parent2 evoli.Individual) (child1, child2 evoli.Individual, err error) {
+	fIndiv1, _ := parent1.(*HIndividual)
+	fIndiv2, _ := parent2.(*HIndividual)
+	w := 0.1 + 0.8*rand.Float64()
 	return &HIndividual{
-		x: []float64{(fIndiv1.x[0] + fIndiv2.x[0]) / 2, (fIndiv1.x[1] + fIndiv2.x[1]) / 2},
-		v: []float64{(fIndiv1.v[0] + fIndiv2.v[0]) / 2, (fIndiv1.v[1] + fIndiv2.v[1]) / 2},
-	}, nil
+			x: []float64{w*fIndiv1.x[0] + (1-w)*fIndiv2.x[0], w*fIndiv1.x[1] + (1-w)*fIndiv2.x[1]},
+			v: []float64{w*fIndiv1.v[0] + (1-w)*fIndiv2.v[0], w*fIndiv1.v[1] + (1-w)*fIndiv2.v[1]},
+		}, &HIndividual{
+			x: []float64{(1-w)*fIndiv1.x[0] + w*fIndiv2.x[0], (1-w)*fIndiv1.x[1] + w*fIndiv2.x[1]},
+			v: []float64{(1-w)*fIndiv1.v[0] + w*fIndiv2.v[0], (1-w)*fIndiv1.v[1] + w*fIndiv2.v[1]},
+		}, nil
 }
 
 type HEvaluater struct {
diff --git a/genetic.go b/genetic.go
index e25d1ef..74b3591 100644
--- a/genetic.go
+++ b/genetic.go
@@ -47,15 +47,15 @@ func (g *genetic) Next() error {
 	if deads != nil {
 		deads.Close()
 	}
-	newBorns, err := g.crossovers(survivors)
+	offsprings, err := g.crossovers(survivors)
 	if err != nil {
 		return err
 	}
-	newBorns, err = g.mutations(newBorns)
+	offsprings, err = g.mutations(offsprings)
 	if err != nil {
 		return err
 	}
-	survivors.Add(newBorns.Slice()...)
+	survivors.Add(offsprings.Slice()...)
 	g.pop = survivors
 	return nil
 }
@@ -88,15 +88,15 @@ func (g *genetic) evaluation(pop Population) error {
 
 func (g *genetic) crossovers(pop Population) (Population, error) {
 	var (
-		newBorns   = NewPopulation(pop.Cap() - pop.Len())
+		capacity   = pop.Cap() - pop.Len()
+		offsprings = NewPopulation(capacity)
 		mut        sync.Mutex
-		capacity   = newBorns.Cap()
 		wg         = sync.WaitGroup{}
 		bubbledErr error
 	)
-	for index := 0; index < capacity; index++ {
+	for index := 0; index < capacity; index += 2 {
 		wg.Add(1)
-		go func() {
+		go func(index int) {
 			defer wg.Done()
 			var i, j = rand.Intn(pop.Len()), rand.Intn(pop.Len())
 			if i == j {
@@ -108,21 +108,24 @@ func (g *genetic) crossovers(pop Population) (Population, error) {
 				}
 			}
 			indiv1, indiv2 := pop.Get(i), pop.Get(j)
-			newBorn, err := g.crosser.Cross(indiv1, indiv2)
+			child1, child2, err := g.crosser.Cross(indiv1, indiv2)
 			if err != nil {
 				bubbledErr = err
 				return
 			}
 			mut.Lock()
-			newBorns.Add(newBorn)
+			offsprings.Add(child1)
+			if index+1 < capacity {
+				offsprings.Add(child2)
+			}
 			mut.Unlock()
-		}()
+		}(index)
 	}
 	wg.Wait()
 	if bubbledErr != nil {
 		return nil, bubbledErr
 	}
-	return newBorns, nil
+	return offsprings, nil
 }
 
 func (g *genetic) mutations(pop Population) (Population, error) {
diff --git a/mock_test.go b/mock_test.go
index 3eb6542..e38b12e 100644
--- a/mock_test.go
+++ b/mock_test.go
@@ -1,10 +1,15 @@
 package evoli
 
+import "math/rand"
+
 type crosserMock struct {
 }
 
-func (c crosserMock) Cross(individual1, individual2 Individual) (Individual, error) {
-	return NewIndividual((individual1.Fitness() + individual2.Fitness()) / 2), nil
+func (c crosserMock) Cross(parent1, parent2 Individual) (child1, child2 Individual, err error) {
+	w := 0.1 + 0.8*rand.Float64()
+	return NewIndividual(w*parent1.Fitness() + (1-w)*parent2.Fitness()),
+		NewIndividual((1-w)*parent1.Fitness() + w*parent2.Fitness()),
+		nil
 }
 
 type evaluaterMock struct {