error in the output of "ss2tf"

Hi,

I use the following command;

[Hgn1,Hgd1]=ss2tf(A_sg,B_sg,C_sg,D_sg,1)

And I get the answer as Hgn1 =

         0   -3.9199   -2.1802  -18.8961  -17.4821   -4.2037   -0.0270   -0.0000
         0    0.5998   -2.8770  -30.8747  -21.4438   -2.8173   -0.0020    0.0000

Hgd1 =

    1.0000    0.9104   17.3228   16.2183    3.6632    2.2271    0.0285    0.0001

However, as I understand I should be getting only 7 elements in each row. (A_sg 7by7 ,B_sg 7 by 7,C_sg 2 by 7 ,D_sg 2 by 7),1 I alwasys get 1 additional element .

What is the reason for this and how can I eliminate this problem

Thank you very much.

Answer 1

[C.J. Harris]

I don't believe there is a problem. The ss2tf function only states that the numerator coefficients are returned in an array with as many rows as there are outputs (two in your case).

Your numerator will always be one longer than the length of your A matrix, while your denumerator will calculated using the 'poly' function, and therefore also appears to be the correct size.

[AVJ]

Thank you very much Chris for helping to understand the logic behind the command.