Hello,
I understand that you are trying to perform mixed-sensitivity loop shaping to design an H-infinity controller for a system specified as a symbolic expression. Following is your code snippet to create the model.
syms s
A=[0 1 0 0; 0 0 0 0; 0 0 0 1; 0 0 29.4 0];
B=[0;1;0;3];
C=[1 0 0 0; 0 0 1 0];
D=[0; 0];
sys = s*eye(4,4)-A;
sys_1 = inv(sys);
SyS = C*sys_1*B+D;
Here, SysS will be created as a symbolic expression.
mixsyn only supports a dynamic system model, such as a state space (ss) or a transfer function (tf), as an input argument. To create a transfer function model, replace symbolic variable s with the variable created using the tf command as shown in the following code snippet.
s = tf('s')
A=[0 1 0 0; 0 0 0 0; 0 0 0 1; 0 0 29.4 0];
B=[0;1;0;3];
C=[1 0 0 0; 0 0 1 0];
D=[0; 0];
sys = s*eye(4,4)-A;
sys_1 = inv(sys);
SyS = C*sys_1*B+D;
You can then use mixsyn function to design your controller.
For more information on how to set up the problem and choose weights, see Mixed-Sensitivity Loop Shaping.
Thanks,
Tushar
