# Artificial viscosity term only for particles nearing one another

The expression for the viscous term above is taken from the wiki at https://github.com/DualSPHysics/DualSPHysics/wiki/3.-SPH-formulation#321-artificial-viscosity

Can a developer please direct me to where this formulation is implemented in the GPU code?

I am essentially interested in looking into this difference between approaching and parting particle pairs. It is a technical question at this moment: knowing how this is done is more important than knowing why. Thanks in advance for directions.

## Comments

If this is not brash of me to presume who has the topmost view to the source code, I would ask if @jmdalonso would please give some directions. Thanks in advance.