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RE: st: beginer's mata function in dofile


From   tashi lama <ltashi32@hotmail.com>
To   <statalist@hsphsun2.harvard.edu>
Subject   RE: st: beginer's mata function in dofile
Date   Tue, 7 Aug 2012 15:23:16 +0000

thanx a lot. This will definitely upp me to try using more mata in my program. The only thing I didn't follow is where you say... it is not necessary to define a program that calls mata functions. Could you elaborate on that?

Thanx
----------------------------------------
> Date: Sat, 4 Aug 2012 14:28:20 +0200
> Subject: Re: st: beginer's mata function in dofile
> From: klein.daniel.81@googlemail.com
> To: statalist@hsphsun2.harvard.edu
>
> Tashi,
>
> your code is kind of confusing. It seems you should have a look into
> Stata ado-programming, before starting with Mata. Your problem is not
> a Mata specific one, but you need to understand the basic principles
> of Stata programming. I recommend reading Baum (2009) chapters 12 and
> 13 for an excellent introduction.
>
> Even though it is not necessary to define a program that calls Mata
> functions, it seems this is what you are trying to do here. Before
> giving a short outline on how to do that, I would like to quote from
> Gould (2006, 114)
>
> "Given trends(), one solution to our problem would be
>
> mata: do_trend_var("b", "bp1 bp2 bp3 bp4 bp5")
>
> _after_ defining
>
> function do_trend_var(string scalar newvarname, string scalar varnames)
> [...]
> (emphasis mine)
>
> So the basic idea should be obvious. You need to define the function
> <do_trend> in Mata, _before_ it can be called from within Stata. This
> is exactly what Stata is telling you (admitted that error messages in
> Mata could be a little more specific from time to time).
>
> Let's get back to your example. First you -capture drop- the program
> <nn>. However this program is never defined, nor is any other program
> (hence my advice to read Baum (2009)). In your code the Mata function
> is defined after the first call to it (ignoring the fact, that your
> code will not define the function, because your -end- does not end
> anything and you do not invoke Mata, definig the function). The
> outline for a program calling Mata functions looks like this
>
> [cap pr drop foo]
> [mata : mata clear]
>
> pr foo
> version 12.1
> my_function()
> [...]
> end
>
> version 12.1
> mata :
> my_function()
> {
> [...]
> }
> end
>
> You will have to save this file as foo.ado, where Stata can find it.
> When you then first call -foo- from within Stata, Stata loads foo.ado
> into memory, meaning that it defines Stata program foo and Mata
> function my_function(). If you are not willing to save the file, you
> can -do- (or -run-) the complete code once. This will also define the
> programs and Mata functions (actually it compiles the Matat function,
> if my understanding of Mata is correct). There are other ways to go,
> but you might want to do some reading on this yourself, maybe starting
> with -help m1_ado-. Either way, the Mata function must be defined
> (compiled), before it is called.
>
> I could go on and wirte more, but I feel this is merely repeating what
> is already documented elsewhere (e.g. type -h mata- and do some hours
> of reading, following the examples given).
>
> Best
> Daniel
>
>
> Baum, C., F.. (2009). An Introduction to Stata Programming. College
> Station, Texas: Stata Press.
> Gould, W. (2006). Mata Matters: Creating new variables - sounds
> boring, isn't. The Stata Journal, 6(1), pp. 112-123.
>
> --
> Hello all,
> I am trying to learn Mata and this is my first do file with mata
> function. I mimicked the code originally written by William Gould of
> StataCorp titled "Mata Matters: Creating new variables-sounds boring,
> isn't".
>
> [...]
> begin do-file mata1.do
> capture program drop nn
> mata: do_trend_var("b", "bp1 bp2 bp3 bp4 bp5")
> list
> end
> function do_trend_var(string scalar newvarname, string scalar varnames)
> {
> real matrix Y
> real colvector b
> real scalar idx
> st_view(Y, ., varnames)
> b =1\2\3\4\5
> idx = st_addvar("float", newvarname)
> st_store(., idx, b)
> }
> exit
> nn
>
> when I run, stata isn't happy and throws back
> <istmt>: 3499 do_trend_var() not found
> r(3499);
>
> Any idea?
> *
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