diff --git a/src/kyupy/wave_sim.py b/src/kyupy/wave_sim.py
index aabb63d..36866c4 100644
--- a/src/kyupy/wave_sim.py
+++ b/src/kyupy/wave_sim.py
@@ -377,9 +377,11 @@ class WaveSimCuda(WaveSim):
 
     def _grid_dim(self, x, y): return cdiv(x, self._block_dim[0]), cdiv(y, self._block_dim[1])
 
-    def c_prop(self, sims=None, seed=1):
+    def c_prop(self, sims=None, seed=1, op_from=0, op_to=None):
         sims = min(sims or self.sims, self.sims)
         for op_start, op_stop in zip(self.level_starts, self.level_stops):
+            if op_from > op_start: continue
+            if op_to is not None and op_to <= op_start: break
             grid_dim = self._grid_dim(sims, op_stop - op_start)
             wave_eval_gpu[grid_dim, self._block_dim](self.ops, op_start, op_stop, self.c, self.c_locs, self.c_caps, self.abuf, int(0),
                 sims, self.delays, self.simctl_int, seed)