How to get ABCD matrix of NLARX model

Dear sir, I have a parallel robotic system,whose forward dynamic modeling has being done using an NLARX model. now i want to use this model for designing a controller. my NLARX model is following form, IDNLARX model with 6 outputs and 6 inputs Input names: u1, u2, u3, u4, u5, u6 Output names: y1, y2, y3, y4, y5, y6 Standard regressors corresponding to the orders: na = [4 0 0 0 0 0; 0 4 0 0 0 0; 0 0 4 0 0 0; 0 0 0 4 0 0; 0 0 0 0 4 0; 0 0 0 0 0 4] nb = [1 0 0 0 0 0; 0 1 0 0 0 0; 0 0 1 0 0 0; 0 0 0 1 0 0; 0 0 0 0 1 0; 0 0 0 0 0 1] nk = [1 0 0 0 0 0; 0 1 0 0 0 0; 0 0 1 0 0 0; 0 0 0 1 0 0; 0 0 0 0 1 0; 0 0 0 0 0 1] what i did was, first i linearize the model using "LM=linapp(m4,umin,umax)" then converted the above model in to continuous form by "LM1=d2c(LM)" then obtained the A,B,C,D matrices using "[A,B,C,D] = ssdata(LM1")but the order of such model is(26X26) how come this? and what initial condition should be taken while using this model in simulink block? is this the right way? is it possible to use an NLARX model block in simulink for any arbitrary inputs for designing the controller? thanks alot rameshkumar