Common variable names#
Unless otherwise stated (in function or class docstrings), this package tries to
adhere to using standard variable names for function and class arguments, and in
example code. For shorthand, the variable
w is used to represent arrays of
phase-space coordinates (e.g., positions _and_ velocities). When representing
only positions, the variable
q is used. For just velocities or momenta, the
v are used.
The arrays and
Quantity objects expected as input and
returned as output throughout
Gala have shapes that follow a particular
convention, unless otherwise specified in function or class docstrings.
For arrays containing coordinate or kinematic information,
axis=0 is assumed
to be the coordinate dimension. For example, for representing 128 different 3D
Cartesian positions, the object should have shape
For collections of orbits, arrays or array-valued objects have three axes: As
axis=0 is assumed to be the coordinate dimension,
interpreted as the time axis, and
axis=2 are the different orbits.
Energy and momentum#
gala documentation and functions often refer to energy and angular
momentum and the respective quantities per unit mass interchangeably. Unless
otherwise specified, all such quantities – e.g., energy, angular momentum,
momenta, conjugate momenta – are in fact used and returned per unit mass.