From b785da87e9271bf851c52e91eb39030a441bda24 Mon Sep 17 00:00:00 2001
From: leo <wanderer@dotya.ml>
Date: Mon, 6 Feb 2023 22:05:01 +0100
Subject: [PATCH] cec2020: implement Weierstrass func

---
 bench/cec2020/basicFunctions.go | 28 +++++++++++++++++++++++++++-
 1 file changed, 27 insertions(+), 1 deletion(-)

diff --git a/bench/cec2020/basicFunctions.go b/bench/cec2020/basicFunctions.go
index 08f1a71..5f01d3d 100644
--- a/bench/cec2020/basicFunctions.go
+++ b/bench/cec2020/basicFunctions.go
@@ -167,4 +167,30 @@ func Schaffer(x []float64) float64 { return 0 }
 
 // Weierstrass is the "Weierstrass Function" of CEC2020 with a=0.5, b=3 and
 // kmax=20.
-func Weierstrass(x []float64) float64 { return 0 }
+func Weierstrass(x []float64) float64 {
+	a := 0.5
+	b := 3.0
+	kmax := 20.0
+	// float64 version of the length of x.
+	fnx := float64(len(x))
+
+	var sum1 float64
+
+	var sum2 float64
+
+	for i := range x {
+		var ksum float64
+
+		for k := 0.0; k < kmax; k++ {
+			ksum += math.Pow(a, k) * math.Cos(2*math.Pi*math.Pow(b, k)*(x[i]+0.5))
+		}
+
+		sum1 += ksum
+	}
+
+	for k := 0.0; k < kmax; k++ {
+		sum2 += math.Pow(a, k) * math.Cos(2*math.Pi*math.Pow(b, k)*0.5)
+	}
+
+	return sum1 - (fnx * sum2)
+}