SkyGrid plots in tracer

[Michael Martin]

Hi all,

I'm working with a Skygrid coalescent model and have some questions about the Ne trajectory plots generated by Tracer. My understanding (maybe wrong!) is that in the Skygrid model Ne is constant between grid points.

However, in the SkyGrid plots generated by Tracer (e.g. those shown here https://beast.community/analysing_beast_output), Ne appears to change in a linear fashion between grid points. This appears to be the case regardless of whether the y-axis is Log(Ne) or Ne, such that the actual Ne trajectories will be different depending on the choice of y-axis. 

I know the SkyGrid model uses a GMRF prior on adjacent elements of the Log(Ne) vector, however, I was under the impression that the actual modeled Ne values between grid points were considered to be constant. 

Is my understanding correct? Why do the Tracer plots not recapitulate the actual modeled Ne values? 

My apologies if I am mistaken about how the model is set up. 

Michael Martin