Polymake under Ubuntu

[DanGrayson]

Add it as a prerequisite to our package:

ubuntu64-1604$ polymake
The program 'polymake' is currently not installed. You can install it by typing:
sudo apt install polymake

(We don't have a way to build it.)

[DanGrayson]

from https://polymake.org/doku.php/download/start :

polymake is part of the package library of the following distributions:

debian >= 9 ubuntu >= 15.10 Fedora Gentoo

[DanGrayson]

It should be added as a prerequisite only if it is installed on the system where we are building M2, so the configure script should check for its existence.

[DanGrayson]

I've added polymake to the install instructions.

[DanGrayson]

This is part of a more general problem, for there are several programs that we use, which might ultimately be available as part of the OS. These include nauty, 4ti2, gfan, and normaliz.

The configure script, in addition to determining whether these programs are present, should determine whether they are part of the OS, for if we are building a binary distribution, then these latter programs should be built if they are not part of the OS, for inclusion in the distribution. (The developer may have installed them independently.)

On the other hand, configure scripts are supposed to be OS independent -- able to adapt to any environment. Hmm.