\subsection{\texttt{gravity\_cube.py}}\label{code:gravity_cube}

\begin{verbatim}
#gravity_cube.py: A bouncing cube simulation using ESyS-Particle
#       Author: D. Weatherley
#       Date: 15 May 2007
#       Organisation: ESSCC, University of Queensland
#       (C) All rights reserved, 2007.
#
#
#import the division module for compatibility between Python 2 and Python 3
from __future__ import division
#import the appropriate ESyS-Particle modules:
from esys.lsm import *
from esys.lsm.util import Vec3, BoundingBox
from esys.lsm.geometry import CubicBlock,ConnectionFinder
from POVsnaps import POVsnaps

#instantiate a simulation object
#and initialise the neighbour search algorithm:
sim = LsmMpi(numWorkerProcesses=1, mpiDimList=[1,1,1])
sim.initNeighbourSearch(
   particleType="NRotSphere",
   gridSpacing=2.5,
   verletDist=0.5
)

#set the number of timesteps and timestep increment:
sim.setNumTimeSteps(10000)
sim.setTimeStepSize(0.001)

#specify the spatial domain for the simulation:
domain = BoundingBox(Vec3(-20,-20,-20), Vec3(20,20,20))
sim.setSpatialDomain(domain)

#add a cube of particles to the domain:
cube = CubicBlock(dimCount=[6,6,6], radius=0.5)
cube.rotate(axis=Vec3(0,0,3.141592654/6.0),axisPt=Vec3(0,0,0))
sim.createParticles(cube)

#create bonds between particles separated by less than the specified
#maxDist:
sim.createConnections(
   ConnectionFinder(
      maxDist = 0.005,
      bondTag = 1,
      pList = cube
   )
)

#specify bonded elastic interactions between bonded particles:
bondGrp = sim.createInteractionGroup(
   NRotBondPrms(
      name = "sphereBonds",
      normalK = 10000.0,
      breakDistance = 50.0,
      tag = 1,
      scaling = True
   )
)

#initialise gravity in the domain:
sim.createInteractionGroup(
   GravityPrms(name="earth-gravity", acceleration=Vec3(0,-9.81,0))
)

#add a horizontal wall to act as a floor to bounce particle off:
sim.createWall(
   name="floor",
   posn=Vec3(0,-10,0),
   normal=Vec3(0,1,0)
)

#specify the type of interactions between wall and particles:
sim.createInteractionGroup(
   NRotElasticWallPrms(
      name = "elasticWall",
      wallName = "floor",
      normalK = 10000.0
   )
)

#add local viscosity to simulate air resistance:
sim.createInteractionGroup(
    LinDampingPrms(
        name="linDamping",
        viscosity=0.1,
        maxIterations=100
    )
)

#add a POVsnaps Runnable:
povcam = POVsnaps(sim=sim, interval=100)
povcam.configure(lookAt=Vec3(0,0,0), camPosn=Vec3(14,0,14))
sim.addPostTimeStepRunnable(povcam)

#execute the simulation
sim.run()
\end{verbatim}

