def P(f):
"""
Pressure
"""
pres = f['rho'] * f['cs']**2
if 'dustFrac' in f.all_keys():
pres *= (1 - f['dustFrac'])
pres_unit = sutil.get_snap_unit(f, 'pres_unit')
return pres.in_units(pres_unit)
def u_smoothlength(f):
"""
Returns the auxilliary array of the same name (excluding the 'u_' prefix)
with units inferred from the runtime parameters.
"""
array_name = 'smoothlength'
if not pynbody.units.has_units(f[array_name]):
# Infer units
units = sutil.get_snap_unit(f, 'l_unit')
f[array_name].units = units
return f[array_name]
def cs(f):
"""
Sound speed
"""
if sutil.is_isothermal(f):
gamma = 1.
else:
gamma = sutil.get_snap_gamma(f)
m = sutil.get_snap_mu(f)
v_unit = sutil.get_snap_unit(f, 'v_unit')
c = np.sqrt(kB * f['temp'] * gamma / m).in_units(v_unit)
return c
def u_dustVel(f):
"""
Returns the auxilliary array of the same name (excluding the 'u_' prefix)
with units inferred from the runtime parameters.
"""
array_name = 'dustVel'
if not pynbody.units.has_units(f[array_name]):
# Infer units
units = sutil.get_snap_unit(f, 'v_unit')
f[array_name].units = units
# This is a necessary check -- currently the master branch of pynbody
# cannot load 3D arrays. This has been implemented on branch issue-379
# of ibackus' fork, but the pull request has not been merged
if (np.ndim(f[array_name]) != 2) or (f[array_name].shape[1] != 3):
raise RuntimeError, "dustVel is a 3D array but was not read as one."\
" This is problem with pynbody"
return f[array_name]
def u_dustGrainSize(f):
"""
Returns the dust grain size with units for onefluid dust.
If grain growth is not on, i.e. if there is not a variable dust size,
the dust size is found in the snapshot param
If grain growth is turned on, i.e. if there is a variable grain size,
the 'dustGrainSize' is returned with proper units.
"""
l_unit = sutil.get_snap_unit(f, 'l_unit')
try:
if not pynbody.units.has_units(f['dustGrainSize']):
f['dustGrainSize'].units = l_unit
grainSize = f['dustGrainSize']
except KeyError:
grainSize = sutil.get_snap_param(f, 'dDustSize')
grainSize = SimArray(grainSize * np.ones(len(f)), l_unit)
return grainSize
def roche_rho(f):
r"""
Roche density
.. math::
\rho_{roche} \equiv M_{star}/r^3
where :math:`r` is the distance to the center of mass of the star(s). The
total star mass is used.
"""
parent = sutil.get_parent_snap(f)
if parent != f:
warnings.warn("Accessing stars from parent snapshot")
star_mass = parent.s['mass'].sum()
star_pos = pynbody.analysis.halo.center_of_mass(parent.s)
r_star = np.sqrt(((f['pos'] - star_pos)**2).sum(1))
rho = 16. * star_mass / r_star**3
rho_unit = sutil.get_snap_unit(parent, 'rho_unit')
return rho.in_units(rho_unit)