Al Feiveson <[email protected]> asks,
> [...] Actually, there are some matrices that I form before the
> iterations that I would like to preserve. Instead of "matrix drop
> _all", is there some easily referenced group of matrices (not my
> own) that should be dropped? 
I am afraid not.  It is a fortuitous artifact that -matrix drop _all- solves
the problem.
In the interim before the update, Al can use the Mata function -st_matrix()-
to safely hold matrices in Mata before -matrix drop _all- and restore them to
Stata afterward.  If the row and column stripes are important, Al will need to
also use -st_matrixrowstripe()- and -st_matrixcolstripe()- to save and restore
the stripes.
 
-- Vince 
   [email protected]
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