Diffusion-limited  Aggregation（DLA）扩散限制凝聚，是由Witten和Sander于1981年共同提出来的。其基本思想是：首先置一初始粒子作为种子，在远离种子的任意位置随机产生一个粒子使其做无规行走，直至与种子接触，成为集团的一部分。然后再随机产生一个粒子，重复上述过程，这样就可以得到足够大的DLA团簇。-Diffusion-limited Aggregation (DLA) Diffusion Limitation Cohesion was presented by Witten and Sander in 1981. The basic idea is to first set an initial particle as a seed, at any position away　the seeds randomly generated a particle to make it random walk until the contact with the seeds, as part of the group. And then randomly generate a particle, repeat the process, so you can get enough large DLA clusters.