mixture of delta functions

Spent the day working on a specialization of mixture-of-gaussians (as a model for a distribution function in a high-dimensionality space) to mixture-of-delta-functions (which would have terrible likelihood for any data set except when you consider that there are observational errors). With Bovy's help I realized that the method we published in 2005 in this unlikely place actually doesn't work for the zero-variance corner of model space. Have to figure out why.