origin function: median of the preceding timepoint

[danfrks]

Hello again,

I was wondering if there was a mathematical function which could be assigned to the origin parameter in the prepanel function, which would result in the relative abundance change at a given timepoint calculated from the median abundance at the timepoint preceding it (as opposed to the median of all the timepoints). It would be great if the plot could show the change in abundance in a progressive manner relative to each timepoint.

Many thanks