I am working with the twostep cluster process in SPSS Modeler (Clementine) and trying to get a sense for the distance function used. It is a log-likelihood function (as stated in docs) but I am unsure for even the continuous variables (the function handles continuous and nominal variable) how this is a log likelihood (it is missing most of the elements of a Gaussian). Below is a screen shot of the documentation describing the distance formula.
Has anyone seen the derivation of this distance function?