[GAP Forum] Root systems representation in GAP

[Nikolay Hodyunya]

Hello all,

Could someone explain me please how does the GAP represent root
systems? I'd like to have representation as in Bourbaki IV-VI chapters
(tables at the end of the book). For example, any root of A_n is of
the form e_i - e_j.

For A_3 positive roots subsystem GAP gives me these vectors: [ [ 2,
-1, 0 ], [ -1, 2, -1 ], [ 0, -1, 2 ], [ 1, 1, -1 ], [ -1, 1, 1 ], [ 1,
0, 1 ] ]. What do they mean?

Thanks.