diff --git a/opencl_fdtd/simulation.py b/opencl_fdtd/simulation.py
index 78460ec..525d818 100644
--- a/opencl_fdtd/simulation.py
+++ b/opencl_fdtd/simulation.py
@@ -273,7 +273,24 @@ class Simulation(object):
                                          arguments=', '.join(S_args.keys()))
 
             self.update_S = lambda e: S_update(*S_args.values(), wait_for=e)
+    def _create_eps(self, epsilon: List[numpy.ndarray]):
+        if len(epsilon) != 3:
+            raise Exception('Epsilon must be a list with length of 3')
+        if not all((e.shape == epsilon[0].shape for e in epsilon[1:])):
+            raise Exception('All epsilon grids must have the same shape. Shapes are {}', [e.shape for e in epsilon])
+        if not epsilon[0].shape == self.shape:
+            raise Exception('Epsilon shape mismatch. Expected {}, got {}'.format(self.shape, epsilon[0].shape))
+        self.eps = pyopencl.array.to_device(self.queue, vec(epsilon).astype(self.arg_type))
 
+    def _create_field(self, initial_value: List[numpy.ndarray] = None):
+        if initial_value is None:
+            return pyopencl.array.zeros_like(self.eps)
+        else:
+            if len(initial_value) != 3:
+                Exception('Initial field value must be a list of length 3')
+            if not all((f.shape == self.shape for f in initial_value)):
+                Exception('Initial field list elements must have same shape as epsilon elements')
+            return pyopencl.array.to_device(self.queue, vec(initial_value).astype(self.arg_type))
 
 def type_to_C(float_type) -> str:
     """