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From: Jan Simon on 17 Jul 2010 12:17
Dear dpb,

> > the possibilities to create an right-upper-triangular matrix with 1
> > column. The best solution is of course to let R equal A, ...
>
> which is also a somewhat peculiar shape for an rut-matrix (excepting one
> special case, of course)... :)

A degenerated triangle is still a triangle.
In this case Q can be assumed to be EYE(size(A, 1)) *or* EYE(1) (also known as [1]).
I think I should publish my fast and memory efficient toolbox for degenerated [1x1] matrices. I've implemented the complete BLAS1/2/3 stuff and a some LAPACK (SVD, EIG, QR, LR, and the functions orgmorgtorg, pargwarg and hirgsirg).

Jan
From: Steven_Lord on 19 Jul 2010 13:43


"Sean Douglas" <seanjdouglas(a)hotmail.com> wrote in message
news:i1qiab$k90$1(a)fred.mathworks.com...
> dpb <none(a)non.net> wrote in message
> <i1qhmc$36e$1(a)news.eternal-september.org>...
>> Sean Douglas wrote:
>> > i want to look at a matab built in function to understand it better.
>> > the particular function is: qr(x,0) , so i think there must be a
>> > built in function called qr.
>> >
>> > can someone tell me how to pull up this build in mfile so i can look at
>> > the code that operates this built in function?
>>
>> type qr.m
>>
>> What you'll see, of course, is the help header including the note at the
>> bottom that QR is a built-in function. That means it is compiled code
>> and the source is not available as for functions implemented as m-files.
>
>
> it thought i should be able to see the built in function because i know
> there have been times when i screw up code from say maybe not defining
> enough variables. when this happens red lettering shows up in the command
> window showing what built in function has the error. When this happens i
> can click on the red letters which indicate the built in function and an
> mfile will come up that i can look at.

I think you're using the term "built in function" to refer to two somewhat
different scenarios.

There are some functions in MATLAB that are implemented as MATLAB function
files that are shipped with MATLAB; those are available for anyone with
access to a MATLAB installation to read. One such example is ODE45.

There are other functions in MATLAB that are implemented as part of the
source code for MATLAB itself, not as MATLAB function files. Those are NOT
available for reading to people outside The MathWorks. One such function is
QR.

Both those types of functions could be considered "built in" to MATLAB, as
they both are included for use with the basic MATLAB installation. If you
click on the hyperlink included in the error message for a function in the
first category, it should bring up the function file in which that function
is implemented. If you click on a similar hyperlink for a function in the
second category, it should bring up the MATLAB script/function file
containing just the help text for that built-in function.

--
Steve Lord
slord(a)mathworks.com
comp.soft-sys.matlab (CSSM) FAQ: http://matlabwiki.mathworks.com/MATLAB_FAQ
To contact Technical Support use the Contact Us link on
http://www.mathworks.com

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