Frame
This string parameter can take
either of the three values: Fixed, Corotating and Guiding-Center (only
the first character matters, and it is case insensitive). When it is
set to 'Fixed', the frame rotates at a constant angular speed,
specified by OmegaFrame (which defaults
to 0, i.e. to a non-rotating
frame). When it is set to 'Corotating', the frame corotates with planet
number 0. If this planet
migrates or has an eccentric orbit, the frame angular speed is not
constant in time. The corresponding acceleration term is conservatively
implemented. The y coordinate
of planet 0 is therefore
always zero in this case. When it is set to 'Guiding-Center', the frame
corotates
with the guiding-center of planet 0.
The frame angular speed therefore varies with time if and only if
planet 0 migrates, and in a
smoother manner than in the 'Corotating' case.