pynbody.analysis.profile.Profile

class pynbody.analysis.profile.Profile(sim, load_from_file=False, ndim=2, type='lin', calc_x=None, weight_by='mass', **kwargs)

Bases: object

A basic profile class for arbitrary profiles. Stores information about bins etc.

Made to work with the pynbody SimSnap instances. The constructor only generates the bins and figures out which particles belong in which bin. Profiles are generated lazy-loaded when a given property is requested.

Input:

sim : a simulation snapshot - this can be any subclass of SimSnap

Optional Keywords:

ndim (default = 2): specifies whether it’s a 2D or 3D profile - in the

2D case, the bins are generated in the xy plane

type (default = ‘lin’): specifies whether bins should be spaced linearly (‘lin’),

logarithmically (‘log’) or contain equal numbers of particles (‘equaln’)

rmin (default = min(x)): minimum radial value to consider

rmax (default = max(x)): maximum radial value to consider

nbins (default = 100): number of bins

binsarray like - predefined bin edges in units of binning quantity. If this

keyword is set, the values of the keywords type, nbins, rmin and rmax will be ignored

calc_x (default = None): function to use to calculate the value

for binning. If None it defaults to the radial distance from origin (in either 2 or 3 dimensions), ut you can specify this function to return any value you want for making profiles along arbitrary axes. Depening on your function, the units of certain profiles (such as density) might not make sense.

weight_by (default = ‘mass’): name of the array to use for weighting

averages across particles in each bin

Output:

a Profile object. To find out which profiles are available, use keys().

Implemented profile functions:

density : density

mass : mass in each bin

mass_enc : enclosed mass

fourierprovides fourier coefficients, amplitude and phase for

m=0 to m=6. To access the amplitude profile of m=2 mode, do p['fourier']['amp'][2,:]

dyntime : dynamical time

g_spherical: GM_enc/r^2

rotation_curve_spherical: rotation curve from vc = sqrt(GM/R) -

can be very wrong!

j_circ : angular momentum of particles on circular orbits

v_circcircular velocity, aka rotation curve - calculated from

the midplane gravity, so this can be expensive

E_circ : energy of particles on circular orbits in the midplane

omega : circular orbital frequency

kappa : radial orbital frequency

beta : 3-D velocity anisotropy parameter

magnitudes : magnitudes in each bin - default band = ‘v’

sb : surface brightness - default band = ‘v’

Additional functions should use the profile_property to yield the desired profile.

Lazy-loading arrays:

The Profile class will automatically compute a mass-weighted profile for any lazy-loadable array of its parent SimSnap object.

Dispersions:

To obtain a dispersion profile, attach a _disp after the desired quantity name.

RMS:

The root-mean-square of a quantity can be obtained by using a _rms suffix

Derivatives:

To compute a derivative of a profile, prepend a d_ to the profile string, as in p['d_temp'] to get a temperature gradient.

Saving and loading previously generated profiles:

Use the write() function to write the current profiles with all the necessary information to a file. Initialize a profile with the load_from_file=True keyword to automatically load a previously saved profile. The filename is chosen automatically and corresponds to a hash generated from the positions of the particles used in the profile. This is to ensure that you are always looking at the same set of particles, centered in the same way. It also means you must use the same centering method if you want to reuse a saved profile.

Methods

create_particle_array(profile_name[, ...])	Create a particle array with the results of the profile calculation.
derivable_keys()	Returns a list of possible profiles
families()	Returns the family of particles used
keys()	Returns a listing of available profile types
write()	Writes all the vital information of the profile to a file.

profile_property

__init__(sim, load_from_file=False, ndim=2, type='lin', calc_x=None, weight_by='mass', **kwargs)

create_particle_array(profile_name, particle_name=None, out_sim=None)

Create a particle array with the results of the profile calculation.

After calling this function, sim[particle_name][i] == profile[profile_name][bin_in_which_particle_i_sits]

If particle_name is not specified, it defaults to the same as profile_name.

derivable_keys()

Returns a list of possible profiles

families()

Returns the family of particles used

keys()

Returns a listing of available profile types

write()

Writes all the vital information of the profile to a file.

To recover the profile, initialize a profile with the load_from_file=True keyword to automatically load a previously saved profile. The filename is chosen automatically and corresponds to a hash generated from the positions of the particles used in the profile. This is to ensure that you are always looking at the same set of particles, centered in the same way. It also means you must use the same centering method if you want to reuse a saved profile.