Thanks for your remind Gao. From this post (The monitored velocity on one inlet planes are not equal to the given ones - #3 by Fei), I get knowledge about inlet velocity UDF if the solver is expected to caculate by DMP. However, in code files like calc_force_dem.f, some variables are added to achieve some functions. Here, two variables ‘Coordination’ and ‘Coor_N’ are introduced for counting the coordination number of a particle. I will run my cases by using DMP. How to edit codes or code files for these two variables? Could you give me an example, thanks.