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# Re: st: how to define a matrix with mathematical expression

 From Nick Cox To statalist@hsphsun2.harvard.edu Subject Re: st: how to define a matrix with mathematical expression Date Mon, 10 Sep 2012 13:49:25 +0100

```I don't think I can add much to my previous post. The key is that
Stata expects to be given a number for each element of a matrix. It
won't do symbolic manipulation, if that is what you are seeking.

If you made concrete what your matrix is, that might help make clear
what you are finding difficult to understand.

Nick

On Mon, Sep 10, 2012 at 1:37 PM, Nina YIN <yinnina.ccer@gmail.com> wrote:
> Hi Nick,
>
>
> Does you mean that I should make these derivations into vectors and
> then define them into matrix?
>
> However, it's a big matrix with size110*110. Also I want to define the
> element "x_{ij}" as
>
> if some condition satisfied, x_{ij}= partial Di/partial Pj;
>
> else  x_{ij}=0.
>
> Therefore, it would be a problem if it need me to define each element by hand.
>
> Do you have any idea about this? Thank you very much!
>
> Best,
> Nina
>
> On Mon, Sep 10, 2012 at 2:27 PM, Nick Cox <njcoxstata@gmail.com> wrote:
>> I think you are correct. If your matrix is a matrix of partial
>> derivatives, you have to do any calculus derivations yourself.
>>
>> Nick
>>
>> On Mon, Sep 10, 2012 at 1:22 PM, Nina YIN <yinnina.ccer@gmail.com> wrote:
>>
>>> I am trying to construct a matrix with elements defined in
>>> mathematical expression. For example, a m*m matrix A with elements
>>> "a_{ij}"=partial Di/ partial Pj. Di (Pj) is the i-th ( j-th ) element
>>> of variable D(P).
>>>
>>> I just know -matrix define and -mkmat, however I didn't find out that
>>> these two commands could help me in this problem. Do I understand it
>>> well?
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