measure "density" of points space for archive

[mmckerns]

This is a bit abstract... but for some given space, one would want to discover where "lots" of points are, and other times where points are "missing". Both are useful. For example, within a given N-dimensional box, one might sample the regions of space to get an idea of how a function performs in each region… one would want to find where there are "holes" in the database, and then sample there next as opposed to randomly selecting a region.