git-svn-id: svn://svn.icms.temple.edu/lammps-ro/trunk@6261 f3b2605a-c512-4ea7-a41b-209d697bcdaa

src/USER-CUDA/comm_cuda.cpp

@@ -55,6 +55,8 @@ enum{SINGLE,MULTI};
 CommCuda::CommCuda(LAMMPS *lmp):Comm(lmp) 
 {
   cuda = lmp->cuda;
+   if(cuda == NULL)
+        error->all("You cannot use a /cuda class, without activating 'cuda' acceleration. Use no '-a' command line argument, or '-a cuda'.");
 
   cu_pbc=NULL;
   cu_slablo=NULL;