[arr] interprets the rows of the matrix as the defining polynomial equations
of the arrangement where the last column will be considered as the constant
terms, i.e. if M is an m*(n+1) matrix we have
H_i = Ker( M_i1*x_1 +...+ M_in*x_n + M_i(n+1) ) for i=1...m and
A = {H_1,...,H_m} the resulting arrangement.