  Matrix divisors are introduced in the work by A.Weil (1938) which is
considered as a starting point of the theory of holomorphic vector bundles on
Riemann surfaces. In this theory matrix divisors play the role similar to the
role of usual divisors in the theory of line bundles. Moreover, they provide
explicit coordinates (Tyurin parameters) in an open subset of the moduli space
of stable vector bundles. These coordinates turned out to be helpful in
integration of soliton equations.
  We would like to gain attention to one more relationship between matrix
divisors of vector G-bundles (where G is a complex semi-simple Lie group) and
the theory of integrable systems, namely to the relationship with Lax operator
algebras. The result we obtain can be briefly formulated as follows: the moduli
space of matrix divisors with certain discrete invariants and fixed support is
a homogeneous space. Its tangent space at the unit is naturally isomorphic to
the quotient space of M-operators by L-operators, both spaces essentially
defined by the same invariants (the result goes back to Krichever, 2001). We
give one more description of the same space in terms of root systems.
