runtime error

from yade import pack, export, plot
from yade import utils, ymport
import math,numpy
#from yade import plot
r_cyl=75
h_cyl=250
psdSizes,psdCumm=[2.36,4.75,6.3,9.5,12.5,19,25],[.365,.512,.596,.77,.864,.974,1] #given psd
area=3.1416*(r_cyl^2) #plate area
freq=0.5 #SGC compaction freq is 30rpm
maxLoad=(6e5)*area #600 kPa is applied vertical load on the specimen
maxLoadlower=maxLoad-100
maxLoadupper=maxLoad+100

cyl1=O.bodies.append(geom.facetCylinder((0,0,0),r_cyl,h_cyl,wallMask=6))
lift_size=30
pred=pack.inCylinder(centerBottom=(0,0,-(h_cyl/2)+1),centerTop=(0,0,lift_size),radius=r_cyl-3)
idAggregate=O.materials.append(FrictMat(density=2600,young=30e9,poisson=.4,frictionAngle=1.0472,label="aggregate")) #frictionangle in rad
sp=pack.SpherePack()
sp.makeCloud((-r_cyl,-r_cyl,-(h_cyl/2)),(r_cyl,r_cyl,h_cyl/2),psdSizes=psdSizes,psdCumm=psdCumm,num=14000, distributeMass=True)
#sp.makeCloud((-r_cyl,-r_cyl,-(h_cyl/2)),(r_cyl,r_cyl,h_cyl/2),rMean=3,rRelFuzz=.5,num=5000)#enforce positive mass
for c,r in sp:
    if pred(c,r):
        O.bodies.append(sphere(c,r,material=idAggregate))

print (len(O.bodies)-1) #no of spheres generated

O.engines=[
   ForceResetter(),
   # sphere, facet, wall
   InsertionSortCollider([Bo1_Sphere_Aabb(),Bo1_Facet_Aabb(),Bo1_Wall_Aabb()]),
   InteractionLoop(
      # the loading plate is a wall, we need to handle sphere+sphere, sphere+facet, sphere+wall
      [Ig2_Sphere_Sphere_ScGeom(),Ig2_Facet_Sphere_ScGeom(),Ig2_Wall_Sphere_ScGeom()],
      #[Ip2_FrictMat_FrictMat_FrictPhys()],
      #[Law2_ScGeom_FrictPhys_CundallStrack()]
      [Ip2_FrictMat_FrictMat_MindlinPhys(en=0.4,es=0.9)],
      [Law2_ScGeom_MindlinPhys_Mindlin()]
   ),
   NewtonIntegrator(gravity=(0,0,-9.81),damping=0.5),
   PyRunner(command='addPlotData()',iterPeriod=10)
]
O.dt=0.005*PWaveTimeStep()
def addPlotData():
   plot.addData(unbalanced=unbalancedForce(),i=O.iter)

plot.plots={'i':('unbalanced',)}
plot.plot()