--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/TimeStepper.jl	Mon Dec 17 14:42:11 2018 +0100
@@ -0,0 +1,60 @@
+abstract type TimeStepper end 
+
+# Returns v and t
+function getState(ts::TimeStepper)
+	error("not implemented")
+end
+
+
+function step(ts::TimeStepper)
+	error("not implemented")
+end
+
+function stepN(ts::TimeStepper,N::Int)
+	for i ∈ 1:N
+		ts.step()
+	end
+end
+
+function stepTo(ts::TimeStepper)
+	error("Not yet implemented")
+end
+
+function evolve(ts::TimeStepper)
+	error("Not yet implemented")
+end
+
+
+mutable struct Rk4 <: TimeStepper
+	F::Function
+	k::Real
+	v::Vector
+	t::Real
+	n::UInt
+
+	function Rk4(F::Function,k::Real,v0::Vector,t0::Real)
+		# TODO: Check that F has two inputs and one output
+		v = v0
+		t = t0
+		n = 0
+		return new(F,k,v,t,n)
+	end
+end
+
+function getState(ts::Rk4)
+	return ts.t, ts.v
+end
+
+function step(ts::Rk4)
+    k1 = ts.F(ts.v,ts.t)
+	k2 = ts.F(ts.v+0.5*ts.k*k1,ts.t+0.5*ts.k)
+	k3 = ts.F(ts.v+0.5*ts.k*k2,ts.t+0.5*ts.k)
+    k4 = ts.F(ts.v+    ts.k*k3,ts.t+    ts.k)
+    ts.v  = ts.v + (1/6)*(k1+2*(k2+k3)+k4)*ts.k
+	
+	ts.n = ts.n + 1
+	ts.t = ts.t + ts.k
+
+	return nothing
+end
+