Skip to content →

neverendingbooks Posts

my first scraper

Published April 2, 2004 by lievenlb

As
far as I know (but I am fairly ignorant) the arXiv does not
provide RSS feeds for a particular section, say mathRA. Still it would be a good idea for anyone
having a news aggregator to follows some weblogs and
news-channels having RSS syndication. So I decided to write one as my
first Perl-exercise and to my own surprise I have after a few hours work
a prototype-scraper for math.RA. It is not yet perfect, I still
have to convert the local URLs to global URLs so that they can be
clicked and at the moment I have only collected the titles, authors and
abstract-links whereas it would make more sense to include the full
abstract in the RSS feed, but give me a few more days…
The
basic idea is fairly simple (and based on an O\’Reilly hack).
One uses the Template::Extract module to
extract the goodies from the arXiv\’s template HTML. Maybe I am still
not used to Perl-documentation but it was hard for me to work out how to
do this in detail either from the hack or the online
module-documentation. Fortunately there is a good Perl Advent
Calendar page giving me the details that I needed. Once one has this
info one can turn it into a proper RSS-page using the XML::RSS-module.
In fact, I spend far
more time trying to get XML::RSS installed under OS X than
writing the code. The usual method, that is via 

iMacLieven:~
lieven$ sudo /usr/bin/perl -MCPAN -e shell Terminal does not support
AddHistory. cpan shell -- CPAN exploration and modules installation
(v1.76) ReadLine support available (try \'install
Bundle::CPAN\') cpan> install XML::RSS

failed and even a
manual install for which the drill is : download the package from CPAN, go to the
extracted directory and give the commands

sudo /usr/bin/perl
Makefile.pl sudo make sudo make test sudo make
install

failed. Also a Google didn\’t give immediate results until
I did find this ADC page which set me on the right track.
It seems that the problem is in installing the XML::Parser for which one first need expat
to be installed. Now, the generic sourceforge page contains a
version for Linux but fortunately it is also part of the Fink
project so I did a

sudo fink install expat

which worked
without problems but afterwards I still was not able to install
XML::Parser because Fink installs everything in the /sw
tree. But after

sudo perl Makefile.pl EXPATLIBPATH=/sw/lib
EXPATINCPATH=/sw/include

I finally got the manual installation
going. I will try to tidy up the script over the weekend…

One Comment

robots.txt

Published March 31, 2004 by lievenlb

I
just finished the formal lecture-part of the course Projects in
non-commutative geometry (btw. I am completely exhausted after this
afternoon\’s session but hopeful that some students actually may do
something with my crazy ideas), springtime seems to have arrived and
next week the easter-vacation starts so it may be time to have some fun
like making a new webpage (yes, again…). At the moment the main
matrix.ua.ac.be page is not really up to standards
and Raf and Hans will be using it soon for the information about the
Liegrits-project (at the moment they just have a beautiful logo). My aim is to make the main page to be the
starting page of the geoMetry site
(guess what M stands for ?) on which I want
to collect as much information as possible on non-commutative geometry.
To get at that info I plan to set some spiders or bots or
scrapers loose on the web (this is just an excuse to force myself
to learn Perl). But it seems one has to follow strict ethical guidelines
in doing so. One of the first sites I want to spider is clearly the arXiv but they have
a scary Robots Beware page! I don\’t know whether their
robots.txt file will allow me to get at any of
their goodies. In a robots.txt file the webmaster can put the
directories on his/her site which are off limits to robots and as I
don\’t want to do anything that may cause that the arXiv is no longer
available to me (or even worse, to the whole department) I better follow
these guidelines. First site on my list to study tomorrow will be The
Web Robots Pages …

Leave a Comment

Borcherds’ monster papers

Published March 27, 2004 by lievenlb


Yesterday morning I thought that I could use some discussions I had a
week before with Markus Reineke to begin to make sense of one
sentence in Kontsevich’ Arbeitstagung talk Non-commutative smooth
spaces :

It seems plausible that Borcherds’ infinite rank
algebras with Monstrous symmetry can be realized inside Hall-Ringel
algebras for some small smooth noncommutative
spaces

However, as I’m running on a 68K RAM-memory, I
didn’t recall the fine details of all connections between the monster,
moonshine, vertex algebras and the like. Fortunately, there is the vast
amount of knowledge buried in the arXiv and a quick search on Borcherds gave me a
list of 17 papers. Among
these there are some delightful short (3 to 8 pages) expository papers
that gave me a quick recap on things I once must have read but forgot.
Moreover, Richard Borcherds has the gift of writing at the same time
readable and informative papers. If you want to get to the essence of
things in 15 minutes I can recommend What
is a vertex algebra? (“The answer to the question in the title is
that a vertex algebra is really a sort of commutative ring.”), What
is moonshine? (“At the time he discovered these relations, several
people thought it so unlikely that there could be a relation between the
monster and the elliptic modular function that they politely told McKay
that he was talking nonsense.”) and What
is the monster? (“3. It is the automorphism group of the monster
vertex algebra. (This is probably the best answer.)”). Borcherds
maintains also his homepage on which I found a few more (longer)
expository papers : Problems in moonshine and Automorphic forms and Lie algebras. After these
preliminaries it was time for the real goodies such as The
fake monster formal group, Quantum vertex algebras and the like.
After a day of enjoyable reading I think I’m again ‘a point’
wrt. vertex algebras. Unfortunately, I completely forgot what all this
could have to do with Kontsevich’ remark…

Leave a Comment