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pNbody/examples/units/setunits_7.py
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setunits_7.py
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#!/usr/bin/env python
from pNbody import *
##############################
# define some system of units
##############################
# output system of units (cgs)
cgs_units = units.UnitSystem('local',[units.Unit_cm,units.Unit_g,units.Unit_s,units.Unit_K])
# gear system of units
params = {}
params['UnitVelocity_in_cm_per_s'] = 20725573.785998672
params['UnitMass_in_g'] = 1.989e+43
params['UnitLength_in_cm'] = 3.085678e+21
gear_units = units.Set_SystemUnits_From_Params(params)
##############################
# compute constants
##############################
# compute mu
Xi=0.76
mu = 4./(8.-5.*(1.-Xi))
# get k (boltzmann) in cgs_units
k = ctes.BOLTZMANN.into(cgs_units)
# get mh (hydrogen mass) in cgs_units
mh = ctes.PROTONMASS.into(cgs_units)
##############################
# specific thermal energy
##############################
T=1e4
ui = 3/2.*k/(mu*mh) *T
##############################
# mass
##############################
mi = 5e-08 # gear_units (500Msol)
mi = mi*gear_units.convertionFactorTo(cgs_units.UnitMass)
##############################
# energy
##############################
Nsn = 5
Nngb= 10.
Esn = Nsn * 1e51 * 0.03 # already in cgs
Esni = Esn/Nngb # already in cgs
##############################
# now compute, all in cgs
##############################
ei = mi*ui
eip= ei + Esni
print "ratio",eip/ei
##############################
# now compute, all in gear
##############################
ui = ui*cgs_units.convertionFactorTo(gear_units.UnitSpecEnergy)
mi = mi*cgs_units.convertionFactorTo(gear_units.UnitMass)
Esni= Esni*cgs_units.convertionFactorTo(gear_units.UnitEnergy)
print "------------"
print ui
print mi
print Esni
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