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From "Phil Steitz" <phil.ste...@gmail.com>
Subject Re: [math] Q-R -decomposition
Date Wed, 29 Mar 2006 22:36:22 GMT
On 3/29/06, Joni Salonen <joni.salonen@gmail.com> wrote:
> Hello! I read from the commons math web page that  Q-R -decomposition
> of matrices is on the wish list. Last night and this afternoon I had
> some free time so I created a clean-room implementation of this
> decomposition using Householder reflectors. The main source of
> information was the description of the algorithm found in Wikipedia:
> http://en.wikipedia.org/wiki/QR_decomposition
>
> I would be interested in working towards getting this algorithm
> integrated in commons-math, but how should I proceed? And does anyone
> have suggestions on how to improve the implementation? The source code
> is downloadable from
> http://www.student.oulu.fi/~jonisalo/QRDecomp.java
> (should be understandable but may not be up to Apache standards yet)

Great!  The first thing to do is to open a Bugzilla ticket and attach
the code to it, with that apache license in the class file headers
(look at any apache java class for an example).   Ideally, you should
also develop and include a test class.  Your main method could be the
start of this.  Have a look at the RealMatrix test classes for
examples.  We can talk further about design here on the list.   From a
quick glance at your code, it looks like you have just implemented the
decomp algorithm statically (which is a great start) and we should
talk about how to structure the API, class name, numerical stability,
and package placement.

Let me know if you need help with mechanics of getting set up with
Junit, maven, Bugzilla, etc.
>
> There is a problem with the current implementation though: it only
> works for non-singular square matrices. What will the usage of the
> algorithm be like? Should the singular and non-square cases be
> implemented, too?

Just handling square, non-singular is a great start, IMO.  Thanks for
your contribution!

Phil

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