# Updating to 0.2¶

Starting with twobody version >=0.1, and thejoker version >=0.2, the following user-facing backwards-incompatible changes were made:

• In the JokerSamples object, and in saved/cached versions, eccentricity was renamed from ecc to e, and the phase or mean anomaly at a reference time was renamed from phi0 to M0.
• The Joker now supports specifying a reference epoch, and the phase M0 is assumed to be at this epoch. Previously, the reference time was always the earliest time in the data, and the phase was assumed to be at MJD=0.

If you updated The Joker and are now having errors reading posterior sample files generated from previous versions of The Joker, or are getting errors related to the twobody package, you have two options:

1. Update both packages and use compatibility functions to convert your old samples file.
2. Install old versions of both packages.

## Option 1: upgrade twobody and thejoker¶

Starting with version 0.2, twobody and thejoker should remain API-compatible. To install the latest versions of both packages, the easiest way is to use pip:

pip install twobody thejoker


If you have done this, and still have cached or saved posterior samples from a previous run of The Joker (i.e. from an older version)

## Option 2: downgrade twobody and thejoker¶

To install versions of twobody and thejoker from before API-breaking changes were made, use:

pip install git+https://github.com/adrn/twobody@fb6578a6ff86cae3ea64338282939e4d1d76afa9