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My statement "You can't affect the precision with which computations are performed. " is technically incorrect (thanks, Nick!) because there are various Mata functions which enable you to increase the accuracy with which a computation is performed (e.g., quadcross()). However, those functions take arguments which are doubles and return objects which are doubles. Thus, you do not have a choice about the accuracy of Mata numeric objects, although you do have alternatives in computing them---and quadcross() will be much better than an explicit matrix multiplication for ill-conditioned matrices.
Kit
Kit Baum | Boston College Economics & DIW Berlin | http://ideas.repec.org/e/pba1.html
An Introduction to Stata Programming | http://www.stata-press.com/books/isp.html
An Introduction to Modern Econometrics Using Stata | http://www.stata-press.com/books/imeus.html
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