[Question #708634]: Enforcing velocity of particle in a periodic cell

```New question #708634 on Yade:

As part of a larger setup, I have an issue in enforcing motion of particles in a periodic cell.

When running the simulation without the periodic cell, the particle moves at the specified velocity for infinite iterations.
However, when the periodic boundary conditions are activated, the simulation runs for some iterations and can then no longer proceed (without pausing or error prompt)
Is there some way to work around this issue or an explanation why this is happening?

In order to summarize the problem, I have attached a shorter script, I kindly ask you to comment and uncomment the periodic boundary section to see the effect.

###########################################################################
from yade import qt, ymport, pack, plot, qt, wrapper
import numpy as np

Mat1 = O.materials.append(FrictMat(young=70e9, frictionAngle=0.8, poisson=0.17,density=2650, label='Mat1'))
O.bodies.append(utils.wall( Vector3(0,0.001,0), axis = 1, sense=0, material = 'Mat1'))

vel = 0.01

# setup the periodic boundary (comment and uncomment)
O.periodic = True
O.cell.hSize = Matrix3(L, 0, 0, 0, h, 0, 0, 0, w)

O.engines = [
ForceResetter(),
InsertionSortCollider([Bo1_Sphere_Aabb(),Bo1_Wall_Aabb()], allowBiggerThanPeriod = True, label="collider"),
InteractionLoop(
[Ig2_Sphere_Sphere_ScGeom(),Ig2_Wall_Sphere_ScGeom()],
[Ip2_FrictMat_FrictMat_MindlinPhys()],
[Law2_ScGeom_MindlinPhys_Mindlin()],
),
NewtonIntegrator(damping=0.1),
PyRunner(iterPeriod=1, command='init(vel)', label='init'),
]
O.dt = 0.8*utils.PWaveTimeStep()
qt.View()
O.pause()

def init(vel):
O.bodies[0].state.vel = [vel,0,0]

###########################################################################

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