# How to understand the paragraph below?

Dear community,
I am trying to reproduce this work, but I really don’t know how to understand the paragraph below:

To acquire the information about velocity gradient, time-averaged velocity contours within the polymer droplet need to be calculated. The calculation method is described as follows. A cylindrical coordinate (r , θ, z) is first built, and its origin is located at the impact point of the droplet. Because the spreading and retraction of the droplet is axisymmetric, the velocity within the droplet is two-dimensional in the cylindrical coordinate, i.e., vr = vr(r, z), vz = vz(r, z), and vθ = 0, where vr is the radial velocity, vθ is the circumferential velocity, and vz is the vertical velocity. Thus, the middle section of the box can be chosen to show the velocity profile, which is divided into 215 × 100 small regions with side lengths of 1σ. Subsequently, the velocity of each small region is calculated every 0.0005τ. The velocity is averaged over a period of 2.5τ.
More details: σ=angstrom, τ=ps. The box is 215×215×100.

I am trying to reproduce this work (output vr and vz contour), I have already known how to transform my coordinate. My questions:
1.“within the polymer droplet need to be calculated” means the calculate group-ID is the polymer droplet only?
2.“A cylindrical coordinate (r , θ, z) is first built, and its origin is located at the impact point of the droplet” , my understanding is to use the compute chunk/atom command, but what’s the right style and settings (my box is 215×215×100 also)?
3.“the middle section of the box can be chosen to show the velocity profile” means the middle slice of the droplet?

You might have omitted a link to the paper you’re trying to reproduce.

Nice to see you again.(￣︶￣)
https://doi.org/10.1021/acs.jpcc.9b02053

I suspect they picked the middle 1 \sigma of the box (i.e. -0.5 < x < 0.5), and then binned that into y and z bins. Then the radial and vertical velocities are just vy and vz. You will have to ask them for their scripts, otherwise it is just too much work trying to reverse-engineer their paper.

But they did build cylindrical coordinate. And
I think they used vr and vz.
That’s true it is hard to reverse😞.