Add functions to produce conformal groups

[fingolfin]

After discussion with @aniemeyer and @danielrademacher we think it would be important to have constructors for conformal orthogonal groups. We could just add them to forms (say in lib/classical.gi). On the long run, perhaps these could also be added to GAP directly...

For this we need paper(s) describing generators for these. If anyone has information on that, please share.

It was suggested that perhaps https://www.maths.usyd.edu.au/u/don/code/Magma/CSpConjugacy.pdf or https://www.maths.usyd.edu.au/u/don/code/Magma/CGOConjugacy.pdf might be a good starting point

@ThomasBreuer might also be interested in this

[fingolfin]

Having a quick look at that source, it seems basically we need to "add in" a diagonal matrix of the form $\mathrm{diag}(a,\dots,a,1,\dots,1)$ where $a$ is a primitive root of the ground field (at least for orthogonal and symplectic groups; I didn't look for the unitary case yet).

[fingolfin]

Magma has these:

ConformalOrthogonalGroup
ConformalOrthogonalGroupMinus
ConformalOrthogonalGroupPlus

ConformalSpecialOrthogonalGroup
ConformalSpecialOrthogonalGroupMinus
ConformalSpecialOrthogonalGroupPlus

ConformalSymplecticGroup

ConformalSpecialUnitaryGroup
ConformalUnitaryGroup

Note that the paper on orthogonal groups linked above is just two pages (and the second only consists of the bibliography).

The paper for the symplectic case is 34 pages, but a good chunk of that is for code for producing conjugacy classes representatives. But the code relevant here is also basically on page 1.

Does someone have a PDF similar to the ones linked above but for the unitary case? Or perhaps we can just easily figure it ourselves along those lines (but it'd be nice to have a concrete reference to point to... though of course the two PDFs linked here aren't great in that regard. If they were at least on arXiv... perhaps we can convince D. E. Taylor to put them there?

[ThomasBreuer]

I am going to make a pull request for the groups described in the abovementioned papers.