Table 1: Comparison of the calculation time of the previous and our method (computation time : sec, bucket size of K-d tree : 10/100, resolutoin of hash table : 30/15).

Num. of particles	Brute-force search	K-d tree:10/100	Hash table:30/15	Our method
10,000	0.003	0.002/0.003	0.001/0.001	0.0005
500,000	0.15	0.13/0.14	0.04/0.04	0.03