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Re: st: re: question about Mata programming


From   "Abdel Rahmen El Lahga" <rahmen.lahga@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: re: question about Mata programming
Date   Thu, 25 Oct 2007 17:55:02 +0200

The solution is given by Bill Gould in this message
www.stata.com/statalist/archive/2006-03/msg01044.html
HTH
AbdelRahmen El Lahga

2007/10/25, Kit Baum <Baum@bc.edu>:
> To more carefully state the point of my last posting:
>
> local macros _are_ dereferenced on demand in Mata's interactive mode.
> Thus
>
> local george 123
> mata:
> a = J(2,2,`george')
> a
> end
>
> works. But that is not very useful, as you can't handily update the
> value of the local macro, which must be defined in Stata (or via
> st_local()). Furthermore, you can't use local macros in Mata
> functions in any useful sense. If you do something like
>
> mata: mata clear
> mata:
> void function eye()
> {
> a = I(`dim')
> a
> }
> end
>
> Mata will not compile the code because `dim' evals to nothing. If you
> preface this with
>
> local dim 2
>
> Mata will gladly compile the code, but will _hard wire_ the number 2
> into the function, and doing
>
> local dim 3
> mata: eye()
>
> will not do what you might think. (This issue---of compile-time
> values---is discussed in the Mata manual). So in summary: don't try
> to use local macros in Mata. Use Mata to access locals and create and
> store new values in Stata's macros, but don't try to use them as
> counter variables as you do in ado-file code.
>
> Kit
>
>
> Kit Baum, Boston College Economics and DIW Berlin
> http://ideas.repec.org/e/pba1.html
> An Introduction to Modern Econometrics Using Stata:
> http://www.stata-press.com/books/imeus.html
>
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>


-- 
AbdelRahmen El Lahga
*
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