calculate output(y) from a state space model

I have defined a first order system in state space. How can I calculate Y matrix, if X matrix known

X'=Ax+Bu; Y=Cx;

I attempted to convert the system to a transfer function using tf command. Then can calculate output by y= tf * u The output matrix appears to be in tf data type. I would like to have y in the same data type as x. (full m file attached, following code is an extract of the state space portion)

%Filter Parameters
Lf= 8e-3;  % Inductance for output filter
Cf= 400e-6;  % Capacitance for output filter

% state space equations for LC filter
A=[zeros(3,3) eye(3)/(3*Cf) -eye(3)/(3*Cf); -eye(3)/Lf zeros(3,3) zeros(3,3);
eye(3,3)/Lload zeros(3,3) -eye(3)*Rload/Lload];    % systemmatrix
B=[zeros(3,3); eye(3)/Lf; zeros(3,3)];      % coefficient for thecontrol variable u
C=eye(9);       % coefficient for the output y
D=[zeros(9,3)];   % coefficient for the output y
Ks = 1/3*[-1 0 1; 1 -1 0; 0 1 -1];    % Conversion matrix to transform [iiAB iiBC iiCA] to [iiA iiB iiC]

%Transfer function for inverter output stage
sys= ss(A,B,C,D);
H=tf(sys);

% calculating filtered output
Y=H(1,1) * V_AB;

Answer 1

[Honglei Chen]

Once you get the model, sys, you can use lsim to simulate the system behavior. You can find details here

http://www.mathworks.com/help/control/ref/lsim.html

HTH

[Rashmil Dahanayake]

Thanks. [y t]=lsim(sys,u,t) command worked well.