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Author: lievenlb

now I see you, now I don’t

Published February 3, 2004 by lievenlb

For
someone as clumsy as me, it is no real surprise to loose one in three
hard disks, but what happened yesterday was a bit puzzling at first. I
tried to replace the original 4 Gb hard disk of an original iMac (a tray
loading iMac) following the instructions of the MacWorld : how to upgrade an iMac-page I used last
time together with Jan to replace two hard disks in slot-loading iMacs.
The whole process is a bit scary : unplug 4 connections, remove the
motherboard, remove the CD-driver in order to get at the hard disk, but
to my own surprise I managed to do all this fairly quickly and replaced
the hard disk by a 120 Gb Seagate Barracuda hard disk. I
put the iMac back together and started up from the OS 9 CD (last time I
forgot this and it is becoming fairly impossible to get a working
System9 defacto on 10.3). I opened DiskUtility and to my surprise the
utility found the new disk, so I managed to install everything properly.
I could even initialize and partition the disk (to run OS X on a first
generation iMac one needs to install it on a partition which is no
larger than 8 Gb) in two partitions (one 8Gb, the other the rest) and
installed System9 on the first partition. So far, so good but when I
restarted the iMac, a blinking question-mark appeared on the screen
indicating that it could not find the installed System9! Then I tried to
start-up from the 10.3-installation disk, started up the DiskUtility and
this time it found no hard disk at all. So I started up again from the
System9 CD and the two partitions appeared on my Desktop, seemingly in
perfect order. What was going on? There was an hard disk, I put System9
on one of its partitions but somehow it refused to find it, and starting
from the 10.3 CD it looked as if there was no hard disk whatsoever. If
you are knowledgeable, you know already where the problem was situated
but as I am more a software than a hardware guy I looked for similar
problems on the net and found an entry in which the solution was
obtained by installing System9 on the larger partition. So I tried this,
but again met the same problems.

So it must be a
hardware problem and I downloaded the product manual and began browsing through it until
I found one of these marvelous computer-terms : the master-slave
jumper settings. Who invents this kind of terminology? The
master-slave jumper… Anyway, here are the possibilities for a
Barracuda
I
admit I didn’t look at the jumper-setting when I inserted the hard
disk. The previous two times it was not necessary and I assumed that the
default position would be the master-setting but wasn’t certain. Hence,
there was only one way to find out and that was redoing the whole
replacement-process… So, this morning I did this and found out that
the jumper-settings were set at Cable select which according to
Geert is the best setting for Windows-computers as
they then automatically decide whether to use the disk as master or
slave, so perhaps for Seagate there is some marketing logic in choosing
this as their default setting. Hence, I changed the setting to
master, quickly put back the iMac and in the end discovered that
I was left with two screws… As they must have been the screws
connecting the hard-disk cage to the motherboard I had little choice but
to redo the whole process a third time. Surprisingly, I began to like
the whole procedure, one should be forced as a computer-user to take
your computer apart a couple of time before working on it. Finally, I
tried to install OS X again, the DiskUtility recognized the two
partitions without any problem and the installation went smoothly.
Probably System9 can find a Cable-select connected hard disk, whereas OS
X cannot…

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Singular via GAP on OSX

Published February 2, 2004 by lievenlb

The
GAP-package is very good in working with finite
fields or Abelian extensions of the Rational numbers, but sooner or
later we will need to use the coordinate ring or function field of an
affine variety for which it is hopeless. On the other hand, there is an
excellent free package to do these calculations : Singular.
So, the ideal situation for us would be to be able to access Singular
from within GAP. Fortunately, Marco Costantini and Willem de
Graaf have written such an interface. Here is how to get in working
under OS X : One has to download two files from the Singular Mac OS X download page :
Singular-2-0-4-ppcMac-darwin.tar.gz and
Singular-2-0-4-share.tar.gz. Once they are on your desktop you
can follow the instructions on the INSTALL.html file in the 2-0-4
Folder of the expanded Singular-2-0-4-ppcMac-darwin. Keep the
tarred version and open the INSTALL-file in your browser (to be
able to copy and paste) and open up the Terminal. Do the analog
thing to 

cd /usr/local sudo tar -pxf
/Users/lieven/Desktop/Singular-2-0-4-ppcMac-darwin.tar sudo tar -pxf
/Users/lieven/Desktop/Singular-2-0-4-share.tar

Then
follow the instructions making the symbolic links and you have Singular
working. The next step is to go to the GAP Packages page and go to the
package Singular for full documentation.
To use Singular in a GAP-session, here is an example

gap>
LoadPackage("singular"); 
The GAP interface to Singular 
true 
gap> StartSingular();
I  Started Singular (version 2004) 
gap> SetInfoLevel( InfoSingular, 2 ); 
gap> G:= SymmetricGroup( 3 );; 
gap> R:= PolynomialRing( GF(2), 3 );; 
gap> GeneratorsOfInvariantRing( R, G ); 
[ x_1 x_2 x_3, x_1*x_2 x_1*x_3 x_2*x_3, x_1*x_2*x_3 ] 
gap> I:= Ideal( R, last );; 
gap>GroebnerBasis( I );
I  running GroebnerBasis... I  done
GroebnerBasis. [ x_1 x_2 x_3, x_2^2 x_2*x_3 x_3^2, x_3^3 ] 
gap>
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GAP on OS X

Published January 29, 2004 by lievenlb


GAP the Groups, Algorithms, and Programming-tool
(developed by two groups, one in St. Andrews, the other in Aachen) is
the package if you want to work with (finite or finitely
presented) groups, but it has also some routines for algebras, fields,
division algebras, Lie algebras and the like. For years now it is
available on MacClassic but since the last clean install of my
computer I removed it as I was waiting for a Mac OS X-port to be
distributed soon. From time to time I checked the webpage at gap-system.org
but it seems that no one cared for OS X. For my “The book of
points”-project I need a system to make lots of examples so perhaps
one could just as well install the UNIX-version. Fortunately, I did a
last desperate Google on GAP OS X which brought me to the
Aachen-pages of the GAP-group where one seems to be more Macintosh
minded. The relevant page is the further notes for OS X on the
GAP-installation for UNIX-page. Here is what I did to get GAP running
under OS X. First go to the download page (btw. this page has
version 4.4 whereas St-Andrews is still distributing 4.3) and download
the
files

gap4r4.tar.gz,packages-2004_01_27-11_37_UTC.tar.gz,xtom1r1.tar
.gz

This will give you three tar-files on your Desktop. Fire
up the Terminal and make a new directory /usr/local/lib if
it doesn’t exist yet. Then, go to your Desktop folder and do

sudo
cp gap4r4.tar /usr/local/lib sudo cp xtom1r1.tar /usr/local/lib cd
/usr/local/lib sudo tar xvf gap4r4.tar sudo tar xvf
xtom1r1.tar

Then return to your Desktop Folder and copy the
remaining tar-file in the /usr/local/lib/gap4r4/pkg-folder which
is created by untarring the former two files and untar it as above.
Then, it is time to compile everything (assuming you have installed the
Developer’s tools) and there is one magic OS X-command which will
speedup GAP by 20%. Here is what to do 

cd
/usr/local/lib/gap4r4 sudo ./configure sudo make COPTS="-fast
-mcpu=7450"

and everything will compile nicely. If you
are so lucky as to have a G5-system, you should replace the last command
by sudo make COPTS=”-03″. Finally, get everything in the right
place

cd /usr/local/lib/gap4r4/bin sudo cp gap.sh
/usr/local/bin/gap

and if /usr/local/bin is in
your $PATH then typing gap at the command line will give
you the opening GAP-banner :

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