V forward euler (algorithm-archivists#633)

Author: Julian

.editorconfig

@@ -150,6 +150,10 @@ indent_size = 4
 indent_style = space
 indent_size = 4
 
+# V
+[*.v]
+indent_style = tab
+
 # Whitespace
 [*.ws]
 indent_style = space

book.json

@@ -193,6 +193,10 @@
           "lang": "ss",
           "name": "Scheme"
         },
+        {
+          "lang": "v",
+          "name": "Vlang"
+        },
         {
           "lang": "coffee",
           "name": "CoffeeScript"

contents/forward_euler_method/code/v/euler.v

@@ -0,0 +1,37 @@
+import math
+
+fn forward_euler(timestep f64, n int) []f64 {
+	mut res := [f64(0.0)].repeat(n)
+	res[0] = f64(1)
+	for x := 1; x < n; x++ {
+		res[x] = res[x-1] - 3.0*res[x-1]*timestep
+	}
+	return res
+}
+
+fn check(result []f64, threshold, timestep f64) bool {
+	mut approx := true
+	for x := 0; x < result.len; x++ {
+		solution := math.exp(-3.0 * f64(x) * timestep)
+		if math.abs(result[x]-solution) > threshold {
+			tmp := result[x]
+			println("There is a mismatch: abs($tmp-$solution) > $threshold!")
+			approx = false
+		}
+	}
+	return approx
+}
+
+fn main() {
+	timestep := .01
+	threshold := .01
+	n := 100
+
+	result := forward_euler(timestep, n)
+
+	if check(result, threshold, timestep) {
+		println("All values within threshold")
+	} else {
+		println("Value(s) not within threshold")
+	}
+}

contents/forward_euler_method/forward_euler_method.md

@@ -136,6 +136,8 @@ Full code for the visualization follows:
 [import, lang:"fortran"](code/fortran/euler.f90)
 {% sample lang="go" %}
 [import, lang:"go"](code/golang/euler.go)
+{% sample lang="v" %}
+[import, lang:"v"](code/v/euler.v)
 {% sample lang="asm-x64" %}
 [import, lang:"asm-x64"](code/asm-x64/euler.s)
 {% sample lang="java" %}