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Mata is Stata's matrix language. The Mata Matters column shows how Mata can be used interactively to solve problems and as a programming language to add new features to Stata. In this quarter's column, we investigate underflow and overflow and then delve into the details of how floating-point numbers are stored in the IEEE 754 floating-point standard. We show how to test for overflow and underflow. We demonstrate how to use the %21x format to see underflow and the %16H, %16L, %8H, and %8L formats for displaying the byte content of doubles and floats.

Stsatrisk is a wrapper for sts graph that adds a table to a survival plot with at-risk information, making it easy to create graphs that follow the list of recommendations given by Pocock et al. (2002) for Kaplan–Meier plots. We use stsatrisk to create plots in the desired format with the desired information.

Local polynomial regression is a generalization of local mean smoothing as described by Nadaraya (1964)andWat s on (1964). Instead of fitting a local mean, one instead fits a local pth-order polynomial. Calculations for local polynomial regression are naturally more complex than those for local means, but local polynomial smooths have better statistical properties. The computational complexity may, however, be alleviated by using a Stata plugin. In this article, we describe the locpoly command for performing local polynomial regression. The calculations involved are implemented in both ado-code and with a plugin, allowing the user to assess the speed improvement obtained from using the plugin. Source code for the plugin is also provided as part of the package for this program. Copyright 2003 by StataCorp LP.