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st: Re: how to access a matrix in a plugin


From   Kit Baum <baum@bc.edu>
To   statalist@hsphsun2.harvard.edu
Subject   st: Re: how to access a matrix in a plugin
Date   Tue, 19 Sep 2006 09:07:09 -0400

sacrificial lamb

Don't. If you're using version 9.2, why not do this in Mata? C plugins are cumbersome and platform-specific. The speed penalty of Mata over C code is not likely to be very large on any decently fast machine.

Kit


Kit Baum, Boston College Economics
http://ideas.repec.org/e/pba1.html
An Introduction to Modern Econometrics Using Stata:
http://www.stata-press.com/books/imeus.html


On Sep 17, 2006, at 2:33 AM, Tom wrote:


I have problems to understand the ST_mat_el() and ST_mat_store()
commands that pass matrices between Stata and my plugin. Here is my
example program:

program matrixAtoB
        version 9.2
 tempname inmat outmat
 mat `inmat' = (1,2 \ 3,4)
 mat `outmat ' = ([.,.] \ [.,.])
 plugin call intooutmat, `inmat' `outmat'
 matrix list `B'
end

The task is to pass both matrices (inmat and outmat) to the plugin.
Then access inmat and get all of its contents into a C variable, then
possibly do some computations with this variable in C and finally
store the results (which happen to have the same dimensions as the
inpmat) into outmat so Stata can access the output of my computation.

For now, I can do this with a single elment of inmat:

intooutmat.c :

#include "stplugin.h"

STDLL stata_call(int argc, char *argv[])
        {
	   ST_double z ;
	
		  SF_mat_el( argv[0] , 1 , 2 , &z ) ;
                  SF_mat_store( argv[1] , 1 , 2 , z ) ;

           return(0) ;
       }

This takes the element from the first row second column of inmat, puts
it into z, and then puts z into the first row second column of outmat.
But how can I access the WHOLE matrix inmat in the plugin (not just
element by element) and pout it into outmat?
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