Ask the question about the particle tracing module.

I have a question when I have used particle tracing module(fpt). Because I try to utilize the condition of Particle-Particle Interaction. I don’t know how to define the interaction force of particle.

E is electric field, in fact, I have already calculated through AC/DC module. rij is the distance vector between the center of particle i and the center of particle j.

I know the function of dest, but I don’t understand how to combine vector E(Vx,Vy) and position(qx,qy).