Dear Mr. Stechenko,
the model order reduction algorithms doing exactly what you are
looking for.
And you are right, that you only have to provide the data in the
linear matrix representation
H(z) = N(z)/M(z) = C*(s*E - A)^-1*B + D
or in the time domain representation
Ex'(t) = Ax(t) + Bu(t),
y(t) = Cx(t) + Du(t).
As a result, smaller matrices are computed, which lead to polynomials
in the transfer function of smaller order.
You can also look this up in the documentation of the different model
reduction algorithms in the toolbox by using the "help" command.
Best regards,
Steffen W. R. Werner