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the iTunes hack

Published January 22, 2004 by lievenlb

If you
are interested in getting thousands of mp3-files on your computer
using only 128 Kb of ROM, read on! Yesterday I made my hands dirty and
with Jan’s help upgraded two 6 Gb colored iMacs (a blue and a
pink one) to potential servers for our home-network having a 80 Gb resp.
a 120 Gb hard disk. If you do the installation yourself such an upgrade
costs you roughly 1 Euro/Gigabyte which seems to me like a good
investment. Clearly, you need to know how to do this and be less
hardware-phobic than I am. Fortunately, the first problem is easily
solved. There is plenty of good advice on the net : for the colored
iMacs we used the upgrade an iMac-page of MacWorld. For possible
later use, there is also a page for replacing the hard disk in an old iBook
(which seems already more challenging) and in a flat screen iMac (which seems to be impossible
without proper tools). Anyway, we followed the page and in no time
replaced the hard disks (along the way we made all possible mistakes
like not connecting the new hard disk and then being surprised that the
Disk Utility cannot find it or not putting back the RAM-chips and
panicking when the normal start-up chime was replaced by an aggressive
beep). An unexpected pleasant surprise was that the blue iMac, which I
thought to be dead, revived when we replaced the hard disk.

Back home, I dumped a good part of our CD-collection on the blue
iMac (1440 songs, good for 4.3 days of music and taking up 7.11 Gb of
the vast 120 Gb hard disk) to test the iTunes Central hack
explained by Alan Graham in his six
great tips for homemade dot mac servers. Would I manage to get the
entire collection on my old iBook which had only (after installing all
this WarWalking-software) 800 Mb of free disk space? Here is what
I did :

1. On the iBook (or any machine you want to
play this trick on) go to your Home/Music/iTunes-folder and drag
the two files and one directory it contains to the Trash. Do the
same for the two files com.apple.iTunes.eq.plist and
com.apple.iTunes.plist which are in the
Home/Library/Preferences-folder.

2. On the
iBook, use the Finder/Network-icon to connect to the server
(iMacServer in my case) and browse to the iTunes-folder where you placed
all the music (still, on the iBook in the Finder-window opened when you
connect to iMacServer). Make an Alias of the two files and the
directory in it (click on one of them once, go to the
File-submenu of the Finder and choose Make Alias) which
results in three new entries in the iTunes directory : iTunes 4 Music
Library alias, iTunes 4 Music Library.xml alias and iTunes
4 Music Library alias. Drag these 3 aliases to the
Home/Music/iTunes-folder on the iBook and rename them by removing
the alias-addendum.

3. In the Finder-window on
the iBook corresponding to the iMacServer browse to the
Home/Library/Preferences-folder and drag the two files
com.apple.iTunes.eq.plist and com.apple.iTunes.plist to
the Home/Library/Preferences-folder of the iBook. Launch
iTunes and it will give you access to the whole iTunes-collection
of iMacServer! In all, the three aliases and the 2 copied files take up
128 Kb…

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NOG master class update

Published January 21, 2004 by lievenlb


Yesterday I made a preliminary program for the first two months
of the masterclass non-commutative geometry. It is likely that
the program will still undergo changes as at the moment I included only
the mini-courses given by Bernhard
Keller and Markus Reineke but several other people have
already agreed to come and give a talk. For example, Jacques Alev (Reims),
Tom Lenagan (Edinburgh),
Shahn Majid (London),
Giovanna Carnovale (Padua) among others. And in
may, Fred assures me, Maxim Kontsevich will give a couple of talks.

As for the contents of the two courses I will be
teaching I changed my mind slightly. The course non-commutative
geometry I teach jointly with Markus Reineke and making the program
I realized that I have to teach the full 22 hours before he will start
his mini-course in the week of March 15-19 to explain the few
things he needs, like :

To derive all the
counting of points formulas, I only need from your course:
–
the definition of formally smooth algebras basic properties, like
being
hereditary
– the definition of the component
semigroup
– the fact that dim Hom-dim Ext is constant along
components. This I need
even over finite fields $F_q$, but I
went through your proof in “One quiver”,
and it works. The
key fact is that even over $F_q$, the infinitesimal lifting
property implies smoothness in the sense Dimension of variety =
dimension of
(schematic) tangent space in any $F_q$-valued
point. But I think it’s fine for
the students if you do all
this over C, and I’ll only sketch the (few)
modifications for
algebras over $F_q$.

So my plan is to do all of
this first and leave the (to me) interesting problem of trying to
classify formally smooth algebras birationally to the second
course projects in non-commutative geometry which fits the title
as a lot of things still need to be done. The previous idea to give in
that course applications of non-commutative orders to the resolution of
singularities (in particular of quotient singularities) as very roughly
explained in my three talks on non-commutative geometry@n I now
propose to relegate to the friday afternoon seminar. I’ll be
happy to give more explanations on all this (in particular more
background on central simple algebras and the theory of (maximal)
orders) if other people work through the main part of the paper in the
seminar. In fact, all (other) suggestions for seminar-talks are welcome
: just tell me in person or post a comment to this post.

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Bill Schelter’s Maxima

Published January 20, 2004 by lievenlb

Bill
Schelter was a remarkable man. First, he was a top-class mathematician.
If you allow yourself to be impressed, read his proof of the
Artin-Procesi theorem. Bill was also among the first to take
non-commutative geometry seriously. Together with Mike Artin he
investigated a notion of non-commutative integral extensions and he was
the first to focuss attention to formally smooth algebras (a
suggestion later taken up by a.o. Cuntz-Quillen and Kontsevich) and a
relative version with respect to algebras satisfying all identities of
n x n matrices which (via work of Procesi) led to smooth@n
algebras. To youngsters, he is probably best know as the co-inventor of
Artin-Schelter regular algebras. I still vividly remember an
overly enthusiastic talk by him on the subject in Oberwolfach, sometime
in the late eighties. Secondly, Bill was a genuine Lisp-guru and
a strong proponent of open source software, see for example his
petition against software patents. He maintanind
his own version of Kyoto Common Lisp which developed into Gnu
Common Lisp. A quote on its history :

GCL is
the product of many hands over many years. The original effort was known
as the Kyoto Common Lisp system, written by Taiichi Yuasa and Masami
Hagiya in 1984. In 1987 new work was begun by William Schelter, and that
version of the system was called AKCL (Austin Kyoto Common Lisp). In
1994 AKCL was released as GCL (GNU Common Lisp) under the GNU public
library license. The primary purpose of GCL during that phase of it’s
existence was to support the Maxima computer algebra system, also
maintained by Dr. Schelter. It existed largely as a subproject of
Maxima.

Maxima started as Bill’s version of
Macsyma an MIT-based symbolic computation program to which he
added many routines, one of which was Affine a package that
allowed to do Groebner-like computations in non-commutative
algebras (implementing Bergman’s diamond lemma) and which he
needed to get a grip on 3-dimensional Artin-Schelter regular
algebras. Michel and me convinced Fred to acquire funds to
buy us a work-station (costing at the time 20 to 30 iMacs) and have Bill
flown in from the States with his tape of maxima and let him
port it to our Dec-station. Antwerp was probably for years
the only place in the world (apart from MIT) where one could do
calculations in affine (probably highly illegal at the time).
Still, lots of people benefitted from this, among others Michaela
Vancliff and Kristel Van Rompay in their investigation
of 4-dimensional Artin-Schelter regular algebras associated to an
automorphism of a quadric in three-dimensional projective space.
Yesterday I ran into Bill (alas virtually) by browsing the
crypto-category of Fink. There it was, maxima, Bill’s package! I tried to install it
with the Fink Commander and failed but succeeded from the command line.
So, if you want to have your own version of it type 

sudo fink
install maxima

from the Terminal and it will install without
problems (giving you also a working copy of common lisp). Unfortunately
I do not remember too much of Macsyma or Affine but there is plenty of
documentation on the net. Manuals and user guides can be obtained from
the maxima homepage and the University of Texas
(Bill’s university) maintains an online manual, including a cryptic description of
some Affine-commands. But probably I’ll have to send Michaela an
email asking for some guidance on this… Here, as a tribute to Bill who
died in july 2001 the opening banner 

 iMacLieven:~ lieven$
/sw/bin/maxima Maxima 5.9.0 http://maxima.sourceforge.net 
Distributed under the GNU Public License. 
See the file COPYING. 
Dedicated to the memory of William Schelter. 
This is a development version of Maxima. 
The function bug_report() provides bug reporting information. 
(C1)
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