Problem with idgray and ident tool

Hi, I'm trying to use the system identification tool in order to obtain the space state model the mass spring damper 2Dof system, so i'm trying to work with the grey box model. this is my function

function [A,B,C,D]=identificazioneidgrey(m_1,m_2,b_1,b_2,k_1,k_2,Ts);

A1=[0 0 1 0;0 0 0 1];

A2=[((-k_1-k_2)/m_1) (k_2/m_1) (-(b_1+b_2)/m_1) (b_2/m_1);(k_2/m_2) (-(k_2/m_2)) (b_2/m_2) (-(b_2/m_2))];

A=[A1;A2];

B1=[0 0;0 0];

B2=[(1/m_1) 0;0 (1/m_2)];

B=[B1;B2];

C=[1 0 0 0;0 1 0 0];

D=[0 0;0 0];

end

and this is the idgrey model:

odefun='identificazioneidgrey';

m_1=1;

m_2=2;

b_1=1;

b_2=1;

k_1=1;

k_2=1;

parameters={'m_1','m_2','b_1','b_2','k_1','k_2'};

fcn_type='c';

sys=idgrey(odefun,parameters,fcn_type);

the problem is that in the work space i can't find sys, but only ans, inside ans:Empty linear greay-box model.

I want sys because i have to put it inside the ident tool. Where is the error? What can i do?