Identification by least square method

Identification of Linear system, using a least square method.

Given, input u and output y of linear system and it's order, the function find the Numerator N and Denominator D.
N,D]=mcar(u,y,n,k1,k2)
u : input signal of the system
y : Output signal of the system
n : système order
k1,k2 indices of the first value and the last of vector y.
[N,D]=mcar(u,y,n) the program allows to choose k1 and k2
Important: If the input signal is a constant or a system is instable, the result will be Nan. an idéal input is a random signal.