Porosity of a packing with overlapped particles

Hi,

I defined a function to calculate the porosity of a packing with lots of overlapped particles, because the build-in function "utils.porosity()" always got a negative one. This question (https://answers.launchpad.net/yade/+question/404363) gave me some useful hints.

My own function has a serious error, that is my function always got a same porosity whatever the growFactor is. Here is my code segment:

from yade import utils
from yade import pack
from yade import qt

mat1 = O.materials.append(FrictMat(young=5.0e7,poisson=0.25,density=2640.0,frictionAngle=radians(18)))
pred = pack.inAlignedBox((0,0,0),(0.01,0.01,0.01))
dim = pred.dim()
packing = regularHexa(pred, radius=0.0005,gap=0,material=mat1)
O.bodies.append(packing)

# grow particles in order to get lower porosity
growFactor = 1.5
utils.growParticles(growFactor)

def overlappedPorosity(totVol,density):
 totVol = dim[0]*dim[1]*dim[2]
 mass = sum([b.state.mass for b in O.bodies])*pow(growFactor,-3)
 return (totVol - mass/density)/totVol
print 'The porosity of this packing is:',overlappedPorosity(dim[0]*dim[1]*dim[2],O.materials[0].density)

# 3D view and controller
try:
  qt.Controller()
  qt.View()
except:
  pass

In my function, ''mass = sum([b.state.mass for b in O.bodies])*pow(growFactor,-3)'', because after the packing was generated, the radius of each particle in packing was magnified by growFactor using growParticles.

Any useful advice will be highly appreciated.
Thanks in advance,

Huihuang Xia