add the forward euler method in golang (#485)

* add the forward euler method in golang

* change the name golang to go

Author: Julian

contents/forward_euler_method/code/golang/euler.go

@@ -0,0 +1,39 @@
+package main
+
+import (
+	"fmt"
+	"math"
+)
+
+func forwardEuler(timeStep float64, n int) []float64 {
+	result := make([]float64, n)
+	result[0] = 1
+	for x := 1; x < n; x++ {
+		result[x] = result[x-1] - 3*result[x-1]*timeStep
+	}
+	return result
+}
+
+func check(result []float64, threshold, timeStep float64) bool {
+	approx := true
+	for x := 0.; int(x) < len(result); x++ {
+		solution := math.Exp(-3. * x * timeStep)
+		if math.Abs(result[int(x)]-solution) > threshold {
+			fmt.Println(result[int(x)], solution)
+			approx = false
+		}
+	}
+	return approx
+}
+
+func main() {
+	timeStep, threshold := .01, .01
+	n := 100
+
+	result := forwardEuler(timeStep, n)
+	if check(result, threshold, timeStep) {
+		fmt.Println("All values within threshold")
+	} else {
+		fmt.Println("Value(s) not within threshold")
+	}
+}

contents/forward_euler_method/forward_euler_method.md

@@ -123,6 +123,8 @@ Full code for the visualization follows:
 [import, lang:"swift"](code/swift/euler.swift)
 {% sample lang="f90" %}
 [import, lang:"fortran"](code/fortran/euler.f90)
+{% sample lang="go" %}
+[import, lang:"go"](code/golang/euler.go)
 {% endmethod %}
 
 <script>