Added comment on coeff array copying to GPU for PMLs

gprMax/updates.py

@@ -407,6 +407,8 @@ class CUDAUpdates:
             knlH = self.source_module(bld, options=config.sim_config.devices["nvcc_opts"])
             pml.update_magnetic_dev = knlH.get_function(knl_name)
 
+            # Copy material coefficient arrays to constant memory of GPU - must
+            # be done for each kernel
             self._copy_mat_coeffs(knlE, knlH)
 
     def _set_rx_knl(self):