まず、ひとつグラフを作ります。
V=['P','Q','R','S','T']
E=[['P','Q'],['Q','R'],['R','S'],['S','T'],['T','P'],['P','S'],['Q','T'],['Q','S']]
g=Graph([V,E])
隣接行列
sage: g.adjacency_matrix()
[0 1 0 1 1]
[1 0 1 1 1]
[0 1 0 1 0]
[1 1 1 0 1]
[1 1 0 1 0]
接続行列
sage: g.incidence_matrix()
[1 0 0 0 1 1 0 0]
[1 1 1 1 0 0 0 0]
[0 0 1 0 0 0 1 0]
[0 1 0 0 1 0 1 1]
[0 0 0 1 0 1 0 1]
ラプラシアン行列
sage: g.laplacian_matrix()
[ 3 -1 0 -1 -1]
[-1 4 -1 -1 -1]
[ 0 -1 2 -1 0]
[-1 -1 -1 4 -1]
[-1 -1 0 -1 3]
キルヒホフ行列
sage: g.kirchhoff_matrix()
[ 3 -1 0 -1 -1]
[-1 4 -1 -1 -1]
[ 0 -1 2 -1 0]
[-1 -1 -1 4 -1]
[-1 -1 0 -1 3]
ヘルプによると、ラプラシアン行列とキルヒホフ行列は同じものだそうです。