311,511 research outputs found
Using Regular Expressions for Data Management in Stata
Regular expressions make a number of data management operations involving string variables much easier. They do this by allowing the user to search for (and copy or replace) complex patterns of characters within a string. Examples of when regular expression are useful include extracting zip codes from addresses, reformatting dates if they were entered in an inconsistent manner, and removing excess spaces from string expressions. This presentation will give the user a basic introduction to the use of regular expressions, and the Stata functions related to regular expressions, as well as examples of applications where regular expressions can be used to streamline data management.
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Heights and quadratic forms: on Cassels' theorem and its generalizations
In this survey paper, we discuss the classical Cassels' theorem on existence
of small-height zeros of quadratic forms over Q and its many extensions, to
different fields and rings, as well as to more general situations, such as
existence of totally isotropic small-height subspaces. We also discuss related
recent results on effective structural theorems for quadratic spaces, as well
as Cassels'-type theorems for small-height zeros of quadratic forms with
additional conditions. We conclude with a selection of open problems.Comment: 16 pages; to appear in the proceedings of the BIRS workshop on
"Diophantine methods, lattices, and arithmetic theory of quadratic forms", to
be published in the AMS Contemporary Mathematics serie
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