go(bench): add Rastrigin function defintion+test

algo/algo.go

@@ -90,7 +90,8 @@ func PrepComparisonOfMeans(wg *sync.WaitGroup) (*report.PicList, int) {
 
 	algoCount := len(algos)
 	dimLen := len(bench.Dimensions)
-	benchCount := len(bench.Functions)
+	// without Rastrigin in active duty for the moment.
+	benchCount := len(bench.Functions) - 1
 
 	// note: this is a wee bit ugly.
 	for d := 0; d < dimLen; d++ {
@@ -142,7 +143,8 @@ func DoRandomSearch(wg *sync.WaitGroup, m *sync.Mutex) {
 	printRandomSearch("starting...")
 
 	// funcCount is the number of bench functions available.
-	funcCount := len(bench.Functions)
+	// without Rastrigin in active duty for the moment.
+	funcCount := len(bench.Functions) - 1
 	// stats for the current algo (RandomSearch).
 	algoStats := make([][]stats.Stats, funcCount)
 	// ch serves as a way to get the actual computed output.
@@ -214,7 +216,8 @@ func DoStochasticHillClimbing(wg *sync.WaitGroup, m *sync.Mutex) {
 	printSHC("starting...")
 
 	// funcCount is the number of bench functions available.
-	funcCount := len(bench.Functions)
+	// without Rastrigin in active duty for the moment.
+	funcCount := len(bench.Functions) - 1
 	// stats for the current algo (StochasticHillClimber).
 	algoStats := make([][]stats.Stats, funcCount)
 	// ch serves as a way to get the actual computed output.
@@ -275,7 +278,8 @@ func DoStochasticHillClimbing100Neigh(wg *sync.WaitGroup, m *sync.Mutex) {
 	printSHC("starting...")
 
 	// funcCount is the number of bench functions available.
-	funcCount := len(bench.Functions)
+	// without Rastrigin in active duty for the moment.
+	funcCount := len(bench.Functions) - 1
 	// stats for the current algo (StochasticHillClimber).
 	algoStats := make([][]stats.Stats, funcCount)
 	// ch serves as a way to get the actual computed output.

bench/bench.go

@@ -32,6 +32,9 @@ type funcParams struct {
 	// DeJong2Params is a struct holding the min, max allowed value of inputs
 	// passed to the De Jong 2nd function.
 	DeJong2Params = funcParams{min: -5.0, max: 5.0}
+	// RastriginParams is a struct holding the min, max allowed value of inputs
+	// passed to the Rastrigin function.
+	RastriginParams = funcParams{min: -5.12, max: 5.12}
 )
 
 // Min returns the non-exported "min" field of a funcParams struct.

bench/functions.go

@@ -11,6 +11,7 @@
 	"Schwefel":    Schwefel,
 	"De Jong 1st": DeJong1st,
 	"De Jong 2nd": DeJong2nd,
+	"Rastrigin":   Rastrigin,
 }
 
 // FuncNames represents a numbered list of function name.
@@ -18,6 +19,7 @@
 	0: "Schwefel",
 	1: "De Jong 1st",
 	2: "De Jong 2nd",
+	3: "Rastrigin",
 }
 
 // Function params maps function names to their funcParams for easier iterable
@@ -26,6 +28,7 @@
 	"Schwefel":    SchwefelParams,
 	"De Jong 1st": DeJong1Params,
 	"De Jong 2nd": DeJong2Params,
+	"Rastrigin":   RastriginParams,
 }
 
 // Schwefel computes the value of the Schwefel function for x.
@@ -62,3 +65,20 @@ func DeJong2nd(x []float64) float64 {
 
 	return res
 }
+
+// Rastrigin computes the value of the Rastrigin function for x.
+// ref: https://www.sfu.ca/~ssurjano/rastr.html
+func Rastrigin(x []float64) float64 {
+	var sum float64
+
+	// dimension of vector x.
+	d := float64(len(x))
+
+	for _, xi := range x {
+		sum += math.Pow(xi, 2) - 10*(math.Cos(2*math.Pi*xi))
+	}
+
+	y := (10 * d) + sum
+
+	return y
+}

bench/functions_test.go

@@ -102,3 +102,33 @@ func TestDeJong2nd(t *testing.T) {
 		t.Errorf("incorrect DeJong2nd output, want: %f, got: %f", want, got)
 	}
 }
+
+func TestRastrigin(t *testing.T) {
+	testInput := []float64{
+		-2.7137778065280593,
+		-1.9789783390895765,
+		-4.38267902085263,
+		-4.617877608383319,
+		-2.1529909200665474,
+		-3.801849324611571,
+		2.4968697503272486,
+		-0.27358100201730196,
+		2.0444319451255977,
+		3.8798952350630653,
+		-0.6150024279011337,
+		2.8643010641852413,
+		-0.6692444051928748,
+		4.4649633199687475,
+		3.2510298731558507,
+		-4.2095036422081495,
+		-0.130882052243404,
+		1.2001716295708604,
+		-0.29427650577602193,
+	}
+	want := 343.97127081044846
+	got := Rastrigin(testInput)
+
+	if want != got {
+		t.Errorf("incorrect Rastrigin output, want: %f, got: %f", want, got)
+	}
+}