SPH viscosity

In standard SPH formulation the viscosity term can be calculated in different ways as presented in literature (see Morris, 1997, ‘Modeling Low Reynolds Number Incompressible Flows Using SPH’, J Comput Phys, chapt. 2.6).
Which is the formulation that the PhysX SPH code uses?

Best regards.

Perhaps check out physx::PxsParticleSystemSim::computeViscosityMultiplier and physx::calcForce