CosmoCoffee

Hi,

What exactly is the algorithm used for 2D contouring in cosmomc getdist's matlab scripts?

The algorithm I used before and I think it is sensible is to grid samples on a 2d grid, sort the cells by the density and then go from the densenst to the least dense cell until 68% (95%) of all samples are enclosed and record the density at that point which is then used as contouring level. Is something similar used in getdist?

Yes, where the bin values are given by a Gaussian weighting given by the distance from the bin centre, with appropriate compensation for priors when near sharp prior boundaries. Technically it does it by a binary search on the density rather than sorting for 2D case. See Get2DPlotData. It is not very efficient.

Should check results are stable under increasing the number of bins - smoothing can make contours look larger than they really are, depending on how sharply the likelihood falls off.