adrn / twobody

Solving the gravitational two-body problem.

twobody

A Python package for computing orbits and astronomical observables for binary stars, exoplanets, and other gravitational two-body systems.

License

This project is Copyright (c) Adrian Price-Whelan and licensed under the terms of the MIT license. See the licenses folder for more information.

twobody's Issues

Question Regarding Mean Anomaly Calculation Formula

Hi, I have a question regarding the function c_rv_from_elements in twobody.c. The function is defined as follows:

void c_rv_from_elements(double *t, double *rv, int N_t, double P, double K, double e, double omega, double M0, double t0, double tol, int maxiter) { /* Compute the RV of the primary w.r.t. the system barycenter */ double M, E, f; for (int n=0; n < N_t; n++) { M = 2 * M_PI * (t[n] - t0) / P - M0; E = c_eccentric_anomaly_from_mean_anomaly_Newton1(M, e, tol, maxiter); f = c_true_anomaly_from_eccentric_anomaly(E, e); rv[n] = K * (cos(omega + f) + e * cos(omega)); } }
Could you please explain why the formula M =2𝜋/P *(t-t0) -M0 is used instead of M =2𝜋/P *(t-t0) +M0 ?
Thank you very much for your help!

Add theano ops for kepler problem?

This project might be a good place for @dfm's custom theano ops?

Can't install in python 2.7.15

Running pip install twobody yields the following:

It seems the function invalidate_caches is no longer available in python 2.7.15 and thus, twobody cannot be installed..

Collecting twobody
Using cached https://files.pythonhosted.org/packages/96/7e/5a63dd91f13f8c41f81601a011f0d6990b697ae436c60a8d4ce1f202444f/twobody-0.2.tar.gz
Complete output from command python setup.py egg_info:
Traceback (most recent call last):
File "", line 1, in
File "/private/var/folders/_d/dsf3j7cs2x93bdljc73ljslm0000gn/T/pip-install-dT6MhF/twobody/setup.py", line 18, in
from astropy_helpers.setup_helpers import (register_commands, get_debug_option,
File "/private/var/folders/_d/dsf3j7cs2x93bdljc73ljslm0000gn/T/pip-install-dT6MhF/twobody/astropy_helpers/astropy_helpers/setup_helpers.py", line 25, in
from .distutils_helpers import (add_command_option, get_compiler_option,
File "/private/var/folders/_d/dsf3j7cs2x93bdljc73ljslm0000gn/T/pip-install-dT6MhF/twobody/astropy_helpers/astropy_helpers/distutils_helpers.py", line 18, in
from .utils import silence
File "/private/var/folders/_d/dsf3j7cs2x93bdljc73ljslm0000gn/T/pip-install-dT6MhF/twobody/astropy_helpers/astropy_helpers/utils.py", line 23, in
from importlib import invalidate_caches
ImportError: cannot import name invalidate_caches

----------------------------------------

Command "python setup.py egg_info" failed with error code 1 in /private/var/folders/_d/dsf3j7cs2x93bdljc73ljslm0000gn/T/pip-install-dT6MhF/twobody/

Provide access to Cython API to speed up The Joker

If we provide access to a fast, Cythonized rv_from_elements() function, I think I can speed up The Joker by improving the functions in likelihood.py.

Add support for computing astrometric orbits

We should be able to output:

• full, 6-space position/velocity in Cartesian coordinates
• full, 6-space position/velocity in observed coordinates (astrometric + line-of-sight)
• either (2-, RV, or 4-, astrometric) subspace independently (for speed)

Do we also want to be able to add Earth's parallax, velocity, or are we cool with assuming we'll get positions in the ICRS?

cc @davidwhogg

Functionality to compute transit times and impact parameter

Add initialization from Thiele-Innes components

See appendix of https://iopscience.iop.org/article/10.3847/1538-3881/aa8d6f/pdf

physical type labels

I think they should be ['ptype'], not [ptype], in order for numpydoc xref to link them to Astropy.

Write some documentation

Test against old software

e.g., http://www.astro.gsu.edu/~gudehus/binary.html

Compute time delay vs. time

Input K

Hi Adrian,

Is there currently a way to input the semi-amplitude K in a KeplerOrbit?
Sorry if I missed it in the code.

Thanks!