Saving behavior and information within the algorithm.

[news3083]

I observed that the overall volume changes before and after running the InvasionPercolation algorithm.
Is it a bug, or is it intentional for reasons such as reducing computational costs?
I want to extract information about the volume occupied by the liquid phase at each saturation.
Is there a way to disable this feature?

The detailed code is shown below.

""" relative permeability """
pn["throat.volume"] = op.models.geometry.throat_volume.cylinder(pn,throat_diameter="throat.equivalent_diameter",
throat_length="throat.total_length")
pn.regenerate_models()
air = op.phase.Air(network=pn,name='air')
air['pore.surface_tension'] = 0.072
air["throat.surface_tension"] = 0.072
air['pore.contact_angle'] = 180.0 - 20
air.add_model_collection(op.models.collections.phase.air)
air.add_model_collection(op.models.collections.physics.basic)
air.add_model(propname="throat.entry_pressure",
model=op.models.physics.capillary_pressure.washburn,
surface_tension=air["throat.surface_tension"],
contact_angle = air["throat.contact_angle"],
diameter = "throat.inscribed_diameter")
radius = pn["throat.inscribed_diameter"]/2
air["throat.hydraulic_conductance"] = PI*(radius**4)/(8*air["throat.viscosity"]*pn["throat.total_length"])
air.regenerate_models()

water = op.phase.Water(network=pn,name='water')
water.add_model_collection(op.models.collections.phase.water)
water.add_model_collection(op.models.collections.physics.basic)
water["throat.hydraulic_conductance"] = PI*(R**4)/(8*water["throat.viscosity"]*pn["throat.total_length"])
water.regenerate_models()

print(np.sum(pn["pore.volume"]) + np.sum(pn["throat.volume"]))
"7.570243075320842e-09"

ip_temp = op.algorithms.InvasionPercolation(network=pn, phase=air)
ip_temp.set_inlet_BC(pores=inlet)
ip_temp.run()

print(np.sum(pn["pore.volume"]) + np.sum(pn["throat.volume"]))
"1.0"