Installing IMG on Ubuntu

Installing the GAP IMG package of Laurent Bartholdi on a moderately recent Ubuntu, starting from the standard desktop installation. The following assumes that you have administrator rights, in particular, that you can use the sudo command.

Some websites:

• Ubuntu Linux: https://ubuntu.com/
• Laurent Bartholdi homepage: https://www.uni-math.gwdg.de/laurent/
• GAP (Groups, Algorithms, Programming): https://www.gap-system.org/
• GAP packages:
  • FGA (Free Group Algorithms): http://www.icm.tu-bs.de/ag_algebra/software/FGA/
  • FR (Functionally Recursive Groups): https://gap-packages.github.io/fr/
  • GBNP (Gröbner bases of noncommutative polynomials) http://dam03.win.tue.nl/gbnp/chap0.html – Download link currently broken
  • IMG (Iterated Monodromy Groups): https://gap-packages.github.io/img/
  • LPRES (Nilpotent Quotients of L-Presented Groups) https://gap-packages.github.io/lpres/
  • NQ (Nilpotent Quotients of Finitely Presented Groups) https://gap-packages.github.io/nq/

GAP is included in Ubuntu, but not installed by default. Start by installing it, together with the recommended packages:

sudo apt install gap gap-float

Next are some general system and development tools:

sudo apt install g++ cmake autoconf nodejs

We need a few additional libraries:

sudo apt install libreadline-dev zlib1g-dev libsuitesparse-dev

You can of course combine these all into one sudo apt install command, or install it via your favorite installation tool.

Now it is time to install local GAP packages. The recommended procedure given here installs them in your home directory, so other users will not be able to use these. If you want to install these systemwide, you need to install these in some global directory for GAP packages. By default, local GAP packages reside in $HOME/.gap/pkg/, and if this directory does not exist, you need to create it:

mkdir -p $HOME/.gap/pkg/

Here and below, you can replace $HOME by ~, but there are different tilde characters, creating problems when copy-pasting.

Now we need to download and unpack the GAP packages FGA, FR, GBNP, IMG, LPRES, and NQ, which are not included with Ubuntu. (Currently omitting GBNP because the link seems to be broken.) The last two commands implicitly assume that you have no other files ending in .tar.gz in the same directory. To be safe, you can run all these commands in some temporary directory with nothing important in it.

wget http://www.icm.tu-bs.de/ag_algebra/software/FGA/FGA-1.4.0.tar.gz
wget https://github.com/gap-packages/fr/releases/download/v2.4.8/fr-2.4.8.tar.gz
wget https://github.com/gap-packages/img/releases/download/v0.3.2/IMG-0.3.2.tar.gz
wget https://github.com/gap-packages/lpres/releases/download/v1.0.1/lpres-1.0.1.tar.gz
wget https://github.com/gap-packages/nq/releases/download/v2.5.6/nq-2.5.6.tar.gz
for a in *.tar.gz; do tar xvzf $a -C $HOME/.gap/pkg/ && rm $a; done
rm *.tar.gz

Obviously, if wget fails, you will have to try to get this package in some other way.

Both the NQ and the IMG package have some code that needs to be compiled. First IMG:

cd $HOME/.gap/pkg/IMG-0.3.2/
aclocal && autoconf && automake
./configure --with-gaproot=/usr/lib/gap/
make

Now NQ:

cd $HOME/.gap/pkg/nq-2.5.6/
aclocal && autoconf && automake
./configure --with-gaproot=/usr/lib/gap/
make

If everything succeeded, you should now be ready to use the IMG package. (In the following code block, the $ is the shell command prompt, and gap> is the command prompt for gap. Neither of them should be typed. Make sure not to forget the semicolon at the end of each gap command.)

$ gap
gap> LoadPackage("IMG");
gap> dendrite := PolynomialSphereMachine(2,[1/6]);
gap> P1MapBySphereMachine(dendrite);

This last command should output <z^2+(0.+1.i_z)>, denoting the polynomial f(z) = z²+i

Lukas Geyer geyer@montana.edu