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From: Marko Mijatovic on 10 Jan 2010 15:41
"Matt J " <mattjacREMOVE(a)THISieee.spam> wrote in message <hht3p2$jq2$1(a)fred.mathworks.com>...
> "Marko Mijatovic" <telekineza(a)gmail.com> wrote in message <hht1jo$1oh$1(a)fred.mathworks.com>...
>
> > If I knew how to solve it I would not ask. I reviewed my notebook, and I did not managed to find anything important. I know that is similar to LU factorization (ie, solving n systems), and there I stopped ... so I asked if someone knows to help .... and without stupid answers....
> ==================
>
> Once again, why does MATLAB's qr() function not do what you need?


I cant just type inv qr(A)!!!
From: Steven Lord on 10 Jan 2010 21:15

"Marko Mijatovic" <telekineza(a)gmail.com> wrote in message
news:hide0v$gee$1(a)fred.mathworks.com...
> "Matt J " <mattjacREMOVE(a)THISieee.spam> wrote in message
> <hht3p2$jq2$1(a)fred.mathworks.com>...
>> "Marko Mijatovic" <telekineza(a)gmail.com> wrote in message
>> <hht1jo$1oh$1(a)fred.mathworks.com>...
>>
>> > If I knew how to solve it I would not ask. I reviewed my notebook, and
>> > I did not managed to find anything important. I know that is similar to
>> > LU factorization (ie, solving n systems), and there I stopped ... so I
>> > asked if someone knows to help .... and without stupid answers....
>> ==================
>>
>> Once again, why does MATLAB's qr() function not do what you need?
>
>
> I cant just type inv qr(A)!!!

How did you do this for LU? You took advantage of the fact that A = L*U,
right? How are A, Q, and R related? Can you do something similar?

--
Steve Lord
slord(a)mathworks.com
comp.soft-sys.matlab (CSSM) FAQ: http://matlabwiki.mathworks.com/MATLAB_FAQ


From: Matt J on 11 Jan 2010 04:06
"Marko Mijatovic" <telekineza(a)gmail.com> wrote in message <hide0v$gee$1(a)fred.mathworks.com>...
> "Matt J " <mattjacREMOVE(a)THISieee.spam> wrote in message <hht3p2$jq2$1(a)fred.mathworks.com>...
> > "Marko Mijatovic" <telekineza(a)gmail.com> wrote in message <hht1jo$1oh$1(a)fred.mathworks.com>...

> I cant just type inv qr(A)!!!

To quote your original post, you said you were "just missing matlab code with QR factorization..."

This makes it sounds like the problem you were having is that you did not know how to obtain the QR factorization using MATLAB.

Since the qr() function does this, and if you understand that, it is not clear what further help you were hoping to get from us...
From: Oleg Komarov on 11 Jan 2010 05:10
"Matt J "
> > I cant just type inv qr(A)!!!
>
> To quote your original post, you said you were "just missing matlab code with QR factorization..."
>
> This makes it sounds like the problem you were having is that you did not know how to obtain the QR factorization using MATLAB.
>
> Since the qr() function does this, and if you understand that, it is not clear what further help you were hoping to get from us...

I think he wants to know how, in specific, is achieved the QR decomposition. Since in MATLAB it's a builtin fcn, the code isn't available.
I suggest to look for 'householder reflection' in wikipedia and 'Numerical Computing' by Cleve Moler (MATLAB chief scientist): http://www.mathworks.com/moler/

Oleg
From: John D'Errico on 11 Jan 2010 06:20
"Matt J " <mattjacREMOVE(a)THISieee.spam> wrote in message <hieplr$2ih$1(a)fred.mathworks.com>...
> "Marko Mijatovic" <telekineza(a)gmail.com> wrote in message <hide0v$gee$1(a)fred.mathworks.com>...
> > "Matt J " <mattjacREMOVE(a)THISieee.spam> wrote in message <hht3p2$jq2$1(a)fred.mathworks.com>...
> > > "Marko Mijatovic" <telekineza(a)gmail.com> wrote in message <hht1jo$1oh$1(a)fred.mathworks.com>...
>
> > I cant just type inv qr(A)!!!
>
> To quote your original post, you said you were "just missing matlab code with QR factorization..."
>
> This makes it sounds like the problem you were having is that you did not know how to obtain the QR factorization using MATLAB.
>
> Since the qr() function does this, and if you understand that, it is not clear what further help you were hoping to get from us...

No, I think he does not understand what a qr does.
or how to use the result. He cannot simply type
inv(LU(A)) either and get the results that he would
need.

It is time to go back to the books. A QR is a matrix
factorization. Regardless, he does not want to EVER
compute inv on the results of any of these operators.
For example, he wants to learn how to compute the
inverse of Q, WITHOUT the application of inv. Then
he must use \ (backslash) to deal with R.

If it is a question of wanting to program the QR
itself, then it really is time to return to the books,
as we will not write that code for him, even though
it is not that difficult to write.

John
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