When I code like this:
setExternalVector(*hemocell.lattice,(*hemocell.lattice).getBoundingBox(),
DESCRIPTOR::ExternalField::forceBeginsAt,
plb::Array<T,DESCRIPTOR::d>(poiseuilleForce,0.0,0.0))
I set the poiseuilleForce to all lattices or set the poiseuilleForce to boundaries only?