diff --git a/src/bin/bench.rs b/src/bin/bench.rs
index a82560e..37c2528 100644
--- a/src/bin/bench.rs
+++ b/src/bin/bench.rs
@@ -9,8 +9,9 @@ fn main() {
     let dt = 0.01;
     let eom = model::Lorenz63::default();
     let teo = explicit::rk4(eom, dt);
-    let mut x = arr1(&[1.0, 0.0, 0.0]);
+    let mut buf = explicit::RK4Buffer::new_buffer(&teo);
+    let mut x: Array1<f64> = arr1(&[1.0, 0.0, 0.0]);
     for _ in 0..100_000_000 {
-        teo.iterate(&mut x);
+        teo.iterate_buf(&mut x, &mut buf);
     }
 }
diff --git a/src/explicit.rs b/src/explicit.rs
index b76acde..a1f08c4 100644
--- a/src/explicit.rs
+++ b/src/explicit.rs
@@ -148,27 +148,34 @@ pub struct RK4Buffer<A, D> {
     k3: Array<A, D>,
 }
 
-impl<A, S, D, F> TimeEvolutionBuffered<S, D> for RK4<F, F::Time>
+impl<A, D> RK4Buffer<A, D>
+    where A: Scalar,
+          D: Dimension
+{
+    pub fn new_buffer<T>(t: &T) -> RK4Buffer<A, D>
+        where T: ModelSize<D>
+    {
+        RK4Buffer {
+            x: Array::zeros(t.model_size()),
+            k1: Array::zeros(t.model_size()),
+            k2: Array::zeros(t.model_size()),
+            k3: Array::zeros(t.model_size()),
+        }
+    }
+}
+
+impl<A, S, D, F> TimeEvolutionBuffered<S, D, RK4Buffer<A, D>> for RK4<F, F::Time>
     where A: Scalar,
           S: DataMut<Elem = A>,
           D: Dimension,
           F: Explicit<S, D, Time = A::Real, Scalar = A>
 {
     type Scalar = F::Scalar;
-    type Buffer = RK4Buffer<A, D>;
 
-    fn get_buffer(&self) -> Self::Buffer {
-        RK4Buffer {
-            x: Array::zeros(self.model_size()),
-            k1: Array::zeros(self.model_size()),
-            k2: Array::zeros(self.model_size()),
-            k3: Array::zeros(self.model_size()),
-        }
-    }
 
     fn iterate_buf<'a>(&self,
                        mut x: &'a mut ArrayBase<S, D>,
-                       mut buf: &mut Self::Buffer)
+                       mut buf: &mut RK4Buffer<A, D>)
                        -> &'a mut ArrayBase<S, D> {
         let dt = self.dt;
         let dt_2 = self.dt * into_scalar(0.5);
diff --git a/src/traits.rs b/src/traits.rs
index 16a4a1a..967141a 100644
--- a/src/traits.rs
+++ b/src/traits.rs
@@ -45,21 +45,6 @@ pub trait TimeEvolutionBase<S, D>: ModelSize<D> + TimeStep
     fn iterate<'a>(&self, &'a mut ArrayBase<S, D>) -> &'a mut ArrayBase<S, D>;
 }
 
-/// Time-evolution operator with buffer
-pub trait TimeEvolutionBuffered<S, D>: ModelSize<D> + TimeStep
-    where S: DataMut,
-          D: Dimension
-{
-    type Scalar: Scalar;
-    type Buffer;
-    fn get_buffer(&self) -> Self::Buffer;
-    /// calculate next step
-    fn iterate_buf<'a>(&self,
-                       &'a mut ArrayBase<S, D>,
-                       &mut Self::Buffer)
-                       -> &'a mut ArrayBase<S, D>;
-}
-
 pub trait TimeEvolution<A, D>
     : TimeEvolutionBase<OwnedRepr<A>, D, Scalar = A, Time = A::Real>
     + TimeEvolutionBase<OwnedRcRepr<A>, D, Scalar = A, Time = A::Real>
@@ -68,3 +53,13 @@ pub trait TimeEvolution<A, D>
           D: Dimension
 {
 }
+
+/// Time-evolution operator with buffer
+pub trait TimeEvolutionBuffered<S, D, Buffer>: ModelSize<D> + TimeStep
+    where S: DataMut,
+          D: Dimension
+{
+    type Scalar: Scalar;
+    /// calculate next step
+    fn iterate_buf<'a>(&self, &'a mut ArrayBase<S, D>, &mut Buffer) -> &'a mut ArrayBase<S, D>;
+}