how to modify the linkage function?

Hello,

I want to modify the linkage function so that when centroid-based approaches are used the centroid is computed in a different way (for example the medoid of all points: the data point with the minimum distance to all others).

Also the distance between centroids i don't want it to be always euclidean.

Any idea where i can make these modifications? In the code of linkage function, you are using a recurrence function and is not clear to me where the centroid is computed?

(In the help of linkage for all centroid-based approaches you say to always use euclidean distance, but i guess you mean the distance between centroids is always euclidean? however we are allowed to use in Y any distance we want. Where is that used in centroid-based approaches?).

Thanks for the help, Peter