Just another update

Task/Euler-method/D/euler-method.d

@@ -1,26 +1,22 @@
-import std.stdio, std.range;
+import std.stdio, std.range, std.traits;
 
-/**
-Approximates y(t) in y'(t)=f(t,y) with y(a)=y0 and
-t=a..b and the step size h.
-*/
-void euler(F)(in F f, in double y0,
-              in double a, in double b, in double h) {
+/// Approximates y(t) in y'(t)=f(t,y) with y(a)=y0 and t=a..b and the step size h.
+void euler(F)(in F f, in double y0, in double a, in double b, in double h) @safe
+if (isCallable!F && __traits(compiles, { real r = f(0.0, 0.0); })) {
     double y = y0;
-    foreach (t; iota(a, b, h)) {
+    foreach (immutable t; iota(a, b, h)) {
         writefln("%.3f  %.3f", t, y);
         y += h * f(t, y);
     }
-    writeln("done");
+    "done".writeln;
 }
 
 void main() {
-    /// Example: Newton's cooling law
-    static newtonCoolingLaw(in double time, in double t) {
-        return -0.07 * (t - 20);
-    }
+    /// Example: Newton's cooling law.
+    enum newtonCoolingLaw = (in double time, in double t)
+        pure nothrow @safe @nogc => -0.07 * (t - 20);
 
-    euler(&newtonCoolingLaw, 100, 0, 100,  2);
-    euler(&newtonCoolingLaw, 100, 0, 100,  5);
-    euler(&newtonCoolingLaw, 100, 0, 100, 10);
+    euler(newtonCoolingLaw, 100, 0, 100,  2);
+    euler(newtonCoolingLaw, 100, 0, 100,  5);
+    euler(newtonCoolingLaw, 100, 0, 100, 10);
 }

Task/Euler-method/JavaScript/euler-method.js

@@ -0,0 +1,29 @@
+// Function that takes differential-equation, initial condition,
+// ending x, and step size as parameters
+function eulersMethod(f, x1, y1, x2, h) {
+	// Header
+	console.log("\tX\t|\tY\t");
+	console.log("------------------------------------");
+
+	// Initial Variables
+	var x=x1, y=y1;
+
+	// While we're not done yet
+	// Both sides of the OR let you do Euler's Method backwards
+	while ((x<x2 && x1<x2) || (x>x2 && x1>x2)) {
+		// Print what we have
+		console.log("\t" + x + "\t|\t" + y);
+
+		// Calculate the next values
+		y += h*f(x, y)
+		x += h;
+	}
+
+	return y;
+}
+
+function cooling(x, y) {
+	return -0.07 * (y-20);
+}
+
+eulersMethod(cooling, 0, 100, 100, 10);

Task/Euler-method/R/euler-method.r

@@ -0,0 +1,17 @@
+euler <- function(f, y0, a, b, h)
+{
+  t <- a
+  y <- y0
+
+  while (t < b)
+  {
+    cat(sprintf("%6.3f %6.3f\n", t, y))
+    t <- t + h
+    y <- y + h*f(t, y)
+  }
+}
+
+newtoncooling <- function(time, temp)
+  return(-0.07*(temp-20))
+
+euler(newtoncooling, 100, 0, 100, 10)