add code comment for InputNlist struct

source/lib/include/neighbor_list.h

@@ -11,7 +11,14 @@
 
 namespace deepmd{
 
-// format of the input neighbor list
+// construct InputNlist with the input LAMMPS nbor list info.
+//
+// members
+//  inum, numneigh, firstneigh are provided by LAMMPS.
+//  inum is the number of core region atoms.
+//  ilist is the atoms index array within the core region.
+//  numneigh is the array which indicates each core region atom's neighbor atom number.
+//  firstneigh is two-dimensional array which store each core region atom's neighbor index. 
 struct InputNlist
 {
   int inum;
@@ -32,11 +39,23 @@ struct InputNlist
   ~InputNlist(){};
 };
 
+// construct the InputNlist with a two-dimensional vector.
+// inputs
+//  from_nlist
+//  from_nlist is a two-dimensional vector which stores the neighbor information of the core region atoms.
+// outputs
+//  to_nlist
+//  to_nlist is the InputNlist struct which stores the neighbor information of the core region atoms.
 void convert_nlist(
     InputNlist & to_nlist,
     std::vector<std::vector<int> > & from_nlist
     );
 
+// compute the max number of neighbors within the core region atoms
+// outputs
+//  to_nlist is the InputNlist struct which stores the neighbor information of the core region atoms.
+// returns
+//  integer: max number of neighbors
 int max_numneigh(
     const InputNlist & to_nlist
     );
@@ -64,12 +83,24 @@ build_nlist_cpu(
     const float & rcut);
 
 #if GOOGLE_CUDA || TENSORFLOW_USE_ROCM
+// convert the a host memory InputNlist to a device memory InputNlist.
+// inputs
+//  cpu_nlist, gpu_memory, max_nbor_size
+//  cpu_nlist is the host memory InputNlist struct which stores the neighbor information of the core region atoms.
+//  gpu_memory is the device array which stores the elements of gpu_nlist.
+//  max_nbor_size is the max neighbor size.
+// outputs
+//  gpu_nlist
+//  gpu_nlist is the device memory InputNlist struct which stores the neighbor information of the core region atoms.
 void convert_nlist_gpu_device(
     InputNlist & gpu_nlist,
     InputNlist & cpu_nlist,
     int* & gpu_memory,
     const int & max_nbor_size);
 
+// Reclaim the allocated device memory of struct InputNlist
+// inputs
+//  gpu_nlist is the device memory InputNlist struct which stores the neighbor information of the core region atoms.
 void free_nlist_gpu_device(
     InputNlist & gpu_nlist);