mixture of Gaussians

I started writing a short note on using mixtures of Gaussians to improve two-dimensional image fitting. I realized in writing it that our expansions of the exponential and de Vaucouleurs profiles in terms of concentric Gaussians have an amusing property: They provide (automatically) their own three-dimensional deprojections, in the optically thin limit. That is, a set of concentric, two-dimensional, isotropic Gaussians that make a deVaucouleurs profile (and we have that set) can be the projection of a very simple-to-compute set of concentric, three-dimensional, isotropic Gaussians. That could be amusing. I should also look at fitting mixtures of Gaussians to various three-dimensional profiles too. This reminds me of my (dormant) project (with Jon Barron) to build a three-dimensional model of all Galaxies. But of course the main point of all this is to make image fitting code fast and numerically stable.