vector field analysis

[nosek]

Dear Octave hackers,

I have empirical 2D data describing some planar vector field. 
That is, I have a N x 2 matrix of XY coordinates for N points, and a N x 2
matrix of xy components of vectors, which represent the field's direction
and magnitude in each point appropriately.

Questions:

How can I visualize that kind of field using Octave functions?
On Wikipedia I've seen some output of that sort from Mathematica, for
example http://pl.wikipedia.org/wiki/Grafika:Vectorfield.svg

What kind of analysis can I perform with such data?
How, for instance, could I compute (estimate) divergence of this field, and
deduce therefrom something about the localization of the field's sources?

Do you know any fora over the Internet that could be more adequate to such
problems?

Thank you in advance for any help.
Regards,
Krzysztof Nosek
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