CSC uses combined (i.e. overlapping) Chandra observations for detecting X-ray sources. This allows the catalog to include significantly fainter sources than CSC 1.1. The set of overlapping observation
A previous column (Cox, 2009, Stata Journal 9: 137{157) gave a review of methods for working rowwise in Stata. Here rows means observations in a dataset, and the concern is calculations in each observ
