def forceresolution( numgridptscuberoot, 
	lengthcuberoot ) :
	"""	
	returns the force resolution of the PM part in units of 
	the input boxsize 
	args:
		numgridptscuberoot:
		lengthcuberoot    : 
	return :
		force resolution (distance) in units usef for the 
		box size

	"""

	return lengthcuberoot/numgridptscuberoot