[AJamesPhillips]

I may have misunderstood the boundary_collision.cpp code but I'd interpret this as ignoring the friction value when the boundary condition (BC) is NoSlip?

if (obj->bc == BC::NoSlip) {
    vx_rel = 0;
    vy_rel = 0;
    vz_rel = 0;
} // end BC::NoSlip

In the README, the C++ and Python example code set a friction value when the boundary condition (BC) is NoSlip which as a new user I found confusing:

sim.plates.push_back(std::make_unique<ObjectPlate>(
    /*position*/ 0,
    /*type*/ PlateType::bottom,
    /*BC*/ BC::NoSlip,
    /*friction*/ 0.5
));

sim.add_plate(matter.ObjectPlate(0, matter.PlateType.bottom, matter.BC.NoSlip, 0.5))

I'm not sure if either you'd like to comment to help the user understand that the 0.5 value is friction and that it will be ignored when BC is NoSlip. Or if you'd prefer it was removed.

Amazing library by the way. Thanks so much for developing and sharing it.