Can anyone comment on what's happening with arrays of booleans in Numpy? I don't want to duplicate someone elses effort, but don't mind standing on someone elses shoulders. My application calls for operations on both non-sparse and sparce matrices.

"Rich comparisons" are really only syntactic sugar. For non-sparse matrices the ufuncs greater(a,b) and less(a,b) will do the job. Equivalents for sparse matrices probably exist. -Greg Ball