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st: Re: on symmetry


From   Christopher F Baum <baum@bc.edu>
To   statalist@hsphsun2.harvard.edu
Subject   st: Re: on symmetry
Date   Wed, 11 Jun 2003 07:05:42 -0400

On Wednesday, June 11, 2003, at 02:33 AM, David wrote:

Instead, I'd suggest that Stata develop an internally created and maintained
property for matrices that indicates whether or not it is symmetric.
I ran into this issue a while back when developing outtable, which outputs a matrix as a lower triangle iff symmetric. I thought there was a way to access the internal identifier by which Stata stores only the lower triangle for a matrix which it considers symmetric (e.g. a covariance or correlation matrix). After consulting with Stata's developers, no such luck (there is (or was) no user access to that flag). They suggested that I use the condition
det(mat - mat') to determine whether the matrix was numerically symmetric, which is the test employed by outtable.

Kit

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