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# Re: st: How to return a Mata matrix in Stata

 From Tirthankar Chakravarty To statalist@hsphsun2.harvard.edu Subject Re: st: How to return a Mata matrix in Stata Date Fri, 12 Aug 2011 03:10:24 -0700

```Once you have -st_matrix()-ed your -r()- variables from Mata to within
the Stata -program-, you do not need to re-return- them from within
the -program-. You should simply -return add- like in the code below:

************************************************************
clear*
sysuse auto, clear
keep price length weight

capture mata mata drop theta()
mata
void theta()
{
st_view(test = ., ., .)
test_cov = variance(test)
st_matrix("r(v)", test_cov)
test_eigen = symeigensystem(test_cov, X = ., L = .)
st_matrix("r(eigval)", X)
st_matrix("r(eigvec)", L)
st_numscalar("r(theta)", L/sum(L))
}
end

capture program drop mytheta
program define mytheta, rclass
version 11
mata theta()
ret li
display as txt " theta = " as res r(theta)
end

mytheta
return list
************************************************************

T

On Fri, Aug 12, 2011 at 2:51 AM, Alex Olssen <alex.olssen@gmail.com> wrote:
> Dear Statalisters,
>
> Can anyone help me return some matrices in a Stata program that calls
> Mata?  My plan was to use -st_mata()- to names for the matrices and
> then try a -return matrix- call in Stata.  Any help is appreciated.
> Hopefully once I get my head around Mata I will be able to help some
> people. :)  My code is below.  You can paste it straight into the
> do-file editor and run it.  The problems are in the two lines that are
> commented out.
>
> ************************************************************
> sysuse auto, clear
> keep price length weight
>
> capture program drop mytheta
> program define mytheta, rclass
>        version 11
>        mata theta()
>        display as txt " theta = " as res r(theta)
>        // return matrix eigval = r(eigval)
>        // return matrix eigvec = r(eigvec)
>        return scalar theta = r(theta)
> end
>
> capture mata mata drop theta()
> mata
> void theta()
> {
>        st_view(test = ., ., .)
>        test_cov = variance(test)
>        st_matrix("r(v)", test_cov)
>        test_eigen = symeigensystem(test_cov, X = ., L = .)
>        st_matrix("r(eigval)", X)
>        st_matrix("r(eigvec)", L)
>        st_numscalar("r(theta)", L/sum(L))
> }
> end
>
> mytheta
> ************************************************************
>
>
> Kind regards,
> Alex Olssen
> *
> *   For searches and help try:
> *   http://www.stata.com/help.cgi?search
> *   http://www.stata.com/support/statalist/faq
> *   http://www.ats.ucla.edu/stat/stata/
>

--
Tirthankar Chakravarty
tchakravarty@ucsd.edu
tirthankar.chakravarty@gmail.com

*
*   For searches and help try:
*   http://www.stata.com/help.cgi?search
*   http://www.stata.com/support/statalist/faq
*   http://www.ats.ucla.edu/stat/stata/
```