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Hello,

To shorten the problem, I am giving an example.
I am trying to use the position of particles in the vicinity of an individual particle to define the applied forces on that particle. In this problem, forces on each particle depends on the position of two previous particles. Initial release position of the particles are x=[-.25 0 .25], y=[0 0 -.25] [m]
I will calculate the force only for the third particle. For a total of 3 particles, in the component variables I define:

idx=dest(fpt.pidx)
coef1= (idx==3&&fpt.pidx==2)
coef2= (idx==3&&fpt.pidx==1)
nx1=(dest(qx)-qx)*coef1
nx2=(dest(qx)-qx)*coef2
nx3=nx2-nx1

To probe nx1*nx3, I simply used a user defined force in the particle-particle interactions as Fx= nx1*nx3 and Fy=0
The result at t=0 shows Fx= [0 0 -0.0625] for three particles, which is incorrect, +0.0625 is the correct answer.
I know the units are not match, but it is just to see if variables are working fine, because I still don't know how to probe these variables in output after a number of times that I tried.

I found out that everything under variables will not be calculated separately, and that's the reason behind it (coef1*coef2=0 because of no overlap).
my question is how to store a variable for each particle ( for example for the 1st previous particle and the second one separately) so that when I multiply those two variables only the value would multiply not the conditional statements inside each variable.

Thank you