From Mata scalar to Stata local

[Charlie Joyez]

Dear Statalisters,

I'd like to extract the maximum value of a Matrix (defined in mata) and use it in a Stata if function.
Look at what I've done so far using resindex and st_store commands

quietly {
. mata : A=(0,1\2,0)

. mata : A

mata: MaxA=max(A)

mata: st_matrix("MaxA", MaxA)
capture drop maxVal
mata: resindex = st_addvar("float","maxVal")
mata: st_store((1,rows(MaxA)),resindex,MaxA)
noi su maxVal

if maxVal[1]>1 {
 noi display "the network is weigthed"
}
else{
 noi display "the network is not weigthed"
}
}

Stata returns :

    Variable |       Obs        Mean    Std. Dev.       Min        Max
-------------+--------------------------------------------------------
      maxVal |         1           2           .          2          2

the network is weigthed

So I have capture the maximum value of the matrix A and stored it into a Stata variable.
And the if qualifier returns that the network is weighted, which is the information I'd like to capture.

However, the Stata variable created is a real variable, what I don't need -and could even be cumbersome, even more because of the missing values-, I'd like to store this value (here 2) in a local variable.

Is there a way to do it quicker, and nicer, without passing through a real variable?

I guess I shouldn't use st_store to obtain a local in Stata, but I've try the st_numscalar commands, but it seems to do the other way around, from Stata scalar to mata Matrix.
Thanks,
Charlie

[daniel klein]

mata :
x = 42
st_numscalar("myx", x)
st_local("myx", strofreal(x))
end

display myx
display `myx'

Read the help files one more time. st_numscalar(), st_local() and st_matrix() can all be called with one argument or two. They get a scalar (local or matrix) from Stata in the former case and set these respective elements in the latter.

Best
Daniel

[Charlie Joyez]

Thank you Daniel, for your fast answer,
It does work.

The st_local command is just what I needed.
Moreover, you revealed why the st_numscalar didn't work for me, because I was then calling a local variable (i.e. with the ` ' marks), leading to a blank -which is logical-.
Thanks again,
Best,
Charlie

[Nick Cox]

Pedants' corner:

"local variable": a term best avoided

if in Stata is not a function; here it is a command. (What you used is the if command, and not the if qualifier.)

Conversely st_local() and st_store() are Mata functions!

More at http://www.stata.com/statalist/archi.../msg01258.html