Monday, April 03, 2006

Trends in the signal and Python disappointment


I'm seeing trends of the signal with the resolution of
the source galaxies, the distance (in arcseconds) from
the source to the lens. I see no trends with the seeing,
the redshift of the source, the redshift of the lens, or
deblending (at least the blended flag).

The resolution thing is odd because earlier tests showed
no dependence on it. It may be correlated with the galaxy
density, but in that case there is another variable besides
deblending involved and I don't have a guess yet as to
what it is.


I've been really getting into numerical python and thinking
it is our way to get out from under the IDL yoke. I've
been disappointed, however, with some trends I have seen
among the developers. The first thing I saw is that the
only documentation for Numpy is available only if you
fork over some cash. This seems outrageous considering
one of the whole points of developing this stuff is to get
away from fees like this with Matlab and IDL. That said,
the guy who is charging for this stuff is also one of the
most helpful contributors to the mailing list so it may
all work out in the end. I just think it is a bad example
to set.

The second hit came when reading up on the wonderful
PyTables stuff that is being developed. PyTables is a
python+C library to access the HDF5 api. Most of this is
free, but I found out that the most powerful extensions,
which allow efficient complex searches of the tables, are only going
to be available in a commercial product unless someone else
develops something similar. This crap is happening because
PyTables is released under a BSD license. This license
is not compatible with the GPL (also copyleft) and so is not free
software as I see it. BTW, can someone explain how the Python
license is compatible with GPL yet someone can then license
their Python code under BSD?

I have already put all my personal code under the
GPL which is probably the only thing I will ever license under.
I also will be discussing with my collaborators if the sdssidl
code can also be distributed under GPL.


Hogg said...

I guess you can license code -- ie lists of statements -- differently than the license of the language that compiles/executes those statements.

But there are some serious licensing issues for the FOSS community; I have been thinking about academic licensing that requires citation -- so as to protect academics who write code with a significant fraction of their research time.

Erin Sheldon said...

I don't understand why there is
a problem. I have yet to see any
real flaws in the GPL, and even
GPL 3 is really a step in another
direction (yet compatible) rather
than a fix.