Data update

Task/Euler-method/Dart/euler-method.dart

@@ -0,0 +1,44 @@
+import 'dart:math';
+import "dart:io";
+
+const double k = 0.07;
+const double initialTemp = 100.0;
+const double finalTemp = 20.0;
+const int startTime = 0;
+const int endTime = 100;
+
+void ivpEuler(double Function(double, double) function, double initialValue, int step) {
+  stdout.write(' Step ${step.toString().padLeft(2)}: ');
+  var y = initialValue;
+  for (int t = startTime; t <= endTime; t += step) {
+    if (t % 10 == 0) {
+      stdout.write(y.toStringAsFixed(3).padLeft(7));
+    }
+    y += step * function(t.toDouble(), y);
+  }
+  print('');
+}
+
+void analytic() {
+  stdout.write('    Time: ');
+  for (int t = startTime; t <= endTime; t += 10) {
+    stdout.write(t.toString().padLeft(7));
+  }
+  stdout.write('\nAnalytic: ');
+  for (int t = startTime; t <= endTime; t += 10) {
+    var temp = finalTemp + (initialTemp - finalTemp) * exp(-k * t);
+    stdout.write(temp.toStringAsFixed(3).padLeft(7));
+  }
+  print('');
+}
+
+double cooling(double t, double temp) {
+  return -k * (temp - finalTemp);
+}
+
+void main() {
+  analytic();
+  ivpEuler(cooling, initialTemp, 2);
+  ivpEuler(cooling, initialTemp, 5);
+  ivpEuler(cooling, initialTemp, 10);
+}