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# Re: st: How to solve the matrix equation AX = B for X without using Mata

 From Tirthankar Chakravarty To statalist@hsphsun2.harvard.edu Subject Re: st: How to solve the matrix equation AX = B for X without using Mata Date Thu, 15 Dec 2011 05:30:54 -0800

> Also, a bit of traditional matrix algebra:
>
> AX = B
> X=inv(A)*B

This is the least numerically stable way of computing solutions to a
system of linear equations. See Bill Gould's post linked below.

T

On Thu, Dec 15, 2011 at 5:18 AM, Fernando Rios Avila <f.rios.a@gmail.com> wrote:

> On Thu, Dec 15, 2011 at 8:11 AM, Tirthankar Chakravarty
> <tirthankar.chakravarty@gmail.com> wrote:
>> You might want to reconsider Mata. The syntax is no more complicated,
>> and there are several advantages to doing numerical computations in
>> Mata, with a small overhead:
>>
>> **********************************
>> matrix def A = (0.5, 0.25)'
>> matrix def B =  (10, 0.5 \ 0.5, 15)
>> mata: st_matrix("C", ///
>>        C=lusolve(st_matrix("B"), st_matrix("A")))
>> mat li C
>> **********************************
>> You might also want to read this excellent post by Bill Gould:
>> http://www.stata.com/statalist/archive/2011-02/msg00376.html
>>
>> Unless of course you are constrained by your Stata version...
>>
>> T
>>
>> On Thu, Dec 15, 2011 at 4:46 AM, Tiago V. Pereira
>> <tiago.pereira@mbe.bio.br> wrote:
>>> Dear statalisters,
>>>
>>> I need to perform the division of matrices A/B, and need to solve the
>>> matrix equation AX = B for X.
>>>
>>> Is there a quick way to solve for X without using Mata?
>>>
>>> For example, I have the following matrices:
>>>
>>> matrix A = (0.5, 0.25)
>>> matrix B =  (10, 0.5 \ 0.5, 15)
>>>
>>> and the results should be something like:
>>>
>>> matrix C = (0.05, 0)
>>>
>>>
>>>
>>> Tiago
>>>
>>>
>>> *
>>> *   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/
>>
>>
>>
>> --
>> Tirthankar Chakravarty
>> tchakravarty@ucsd.edu
>> tirthankar.chakravarty@gmail.com
>>
>> *
>> *   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/
>
> *
> *   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/

--
Tirthankar Chakravarty
tchakravarty@ucsd.edu
tirthankar.chakravarty@gmail.com

*
*   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/