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Re: st: Function el() fails


From   "Scott Merryman" <scott.merryman@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Function el() fails
Date   Fri, 15 Aug 2008 21:56:15 -0500

You could use the pseudofunction -matrix()- to force the term p to be
interpreted as a matrix (see [P] page 262, "Name conflicts in
expressions (namespaces)"  and G Kolev's "Stata tip 31: Scalar or
variable?  The problem of ambiguous names", SJ 6,2).

    dis el(matrix(p),1,1)

Scott


On Fri, Aug 15, 2008 at 4:54 PM, Sergiy Radyakin <serjradyakin@gmail.com> wrote:
> Dear All,
>
> after investigating why my program sometimes breaks, I have found a
> problem (observed in Stata 9 and Stata 10 for Windows) with the
> function el(matrixname, row, col ), which could be reproduces with the
> following sequence of commands:
>
>
> // ----- BEGIN -------
>   sysuse auto
>
>   matrix p=1
>   matrix a=p
>
>   matrix dir
>
>   matrix list a
>   di a[1,1]
>   di el(a,1,1)
>
>   matrix list p
>   di p[1,1]
>   di el(p,1,1)
> // ----- END -------
>
> According to the help file for Stata 9:
>
>  el(A,i,j)       the i,j element of A (same as A[i,j])
>
> Note that the program above works for matrix name "a" and not "p".
> This made it difficult to identify the problem. Because the problem is
> observed for some datasets and not for others.
>
> It seems that the namespace of variables and matrix names in Stata is
> overlapping.
> I've met the messages earlier regarding what namespaces are shared,
> but I can't find them at the moment. The manual explicitly defines the
> term "namespace" in the [P] matrix, (page 235 in 10th edition). It
> also mentions that there is a single namespace for scalars and
> matrices, however it does mention variables in a rather confusing
> statement:
>
> "Scalars and matrices share the same namespace; i.e., scalars and
> matrices may have the same names as variables in the dataset, etc.,
> but they cannot have the same names as each other."
>
> Confusion here is that indeed Stata allows me to have a matrix with
> the same name as a variable, but I'd really like the built-in commands
> and functions to be able to WORK with that matrix. (Function el() as
> all functions in Stata is built-in).
>
> I wonder if anyone could elaborate on which namespaces are shared in
> Stata, in particular:
>
> variables
> locals
> globals
> scalars
> matrices
> programs
> classes
> all sort of mata objects
> all sort of graphics related styles, patterns, etc
> ....
> [not sure how long the list is, but the above list is definitely not complete]
>
> I am not sure that the problem above is an intended behavior. In any
> case it makes the case that el(a,1,1) is NOT equivalent to A[1,1]
> against what the help file says.
> If this is not an intended behaviour, can this be fixed?
>
> Thank you,
> Sergiy Radyakin
>
> CC: Stata Technical Support
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