st: re: question about Mata programming

[Kit Baum <baum@bc.edu>]

Xiaoheng listed a chunk of Mata code which wasn't working for him:

-------------------------- mata (type end to exit)
-------------------------------
: for (k=1; k<=2; k++) {
> r`k' = rowmin(D)
> C`k' = J(3 , 3 , 2)
> for (i=1; i<=3; i++) {
> for (j=1; j<=3; j++) {
> if (D[ i , j ] == r`k'[ i , 1 ])
> C`k'[ i , j ] = 1
> D[ i , j ] = D[ i , j ] + 10000
> else C`k'[ i , j ] = 0
'else' found where almost anything else expected
r(3000);

The problem is that you cannot use local macros in Mata. You can  
access Stata's local macros (and change them) but you cannot create  
objects using local (or global) macro names. To Mata,

C = C`k' = C`anythingelse'

If you want multiple objects, you must use other techniques to create  
them.

David Drukker posted a Mata solution to the nearest-neighbor problem  
recently. Have a look at his posting.

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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