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

[Maarten Buis <maartenlbuis@gmail.com>]

You cannot expect much help, since you still have not specified what
it is exactly that you want to do, even though you were explicitly
asked to do so. All we can than do is give you general comments, like:
in Stata you can typically use equations to quickly fill in those 0s.
Moreover, you would typically be able to fill in the rest easily by
using the chain rule. Often the combination of these two tricks
reduces a seemingly huge problem to an easily manageable problem. This
is done a lot in Stata whenever something is done with maximum
likelihood. Whether these tricks also help in your case, we just
cannot say as you did not explain what your problem is.

-- Maarten

On Mon, Sep 10, 2012 at 2:55 PM, Nina YIN wrote:
> Okay, Nick, thank you for your answer,  Symbolic manipulation is
> exactly what I want.
> Maybe I should return to Matlab to deal with it.
>
> On Mon, Sep 10, 2012 at 2:49 PM, Nick Cox <njcoxstata@gmail.com> wrote:
>> 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,
>>>
>>> Thank you for your reply!
>>>
>>> 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?
>> *
>> *   For searches and help try:
>> *   http://www.stata.com/help.cgi?search
>> *   http://www.stata.com/support/statalist/faq
>> *   http://www.ats.ucla.edu/stat/stata/
>
>
>
> --
> Best Regards,
> Nina YIN
>
>
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> *
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-- 
---------------------------------
Maarten L. Buis
WZB
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10785 Berlin
Germany

http://www.maartenbuis.nl
---------------------------------
*
*   For searches and help try:
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*   http://www.stata.com/support/statalist/faq
*   http://www.ats.ucla.edu/stat/stata/