Data commit

Task/Runge-Kutta-method/FutureBasic/runge-kutta-method.basic

@@ -0,0 +1,26 @@
+window 1
+
+def fn dydx( x as double, y as double ) as double = x * sqr(y)
+def fn exactY( x as long ) as double = ( x ^2 + 4 ) ^2 / 16
+
+long i
+double h, k1, k2, k3, k4, x, y, result
+
+h = 0.1
+y = 1
+for i = 0 to 100
+  x = i * h
+  if x == int(x)
+    result = fn exactY( x )
+    print "y("; mid$( str$(x), 2, len$(str$(x) )); ") = "; y, "Error = "; result - y
+  end if
+
+  k1 = h * fn dydx( x, y )
+  k2 = h * fn dydx( x + h / 2, y + k1 / 2 )
+  k3 = h * fn dydx( x + h / 2, y + k2 / 2 )
+  k4 = h * fn dydx( x + h,     y + k3     )
+
+  y = y + 1 / 6 * ( k1 + 2 * k2 + 2 * k3 + k4 )
+next
+
+HandleEvents