Can any body helps me in sorting out my problem of writing the expression in LMI editor window of Robust Control tool box of Matlab?

As per my requirement ,I have written following mat-lab expressions in LMI editor window of robust control tool box of mat-lab, so as to calculate the values of different matrices shown in these expressions according to the restriction imposed on them for optimizing my result. The expressions or different LMI's are as under:

R>0
S>0
Y1>0
Y1*Y4-Y2*Y3>0
Fy~=0
Zy~=0
Zy*Fy'==eye(2)-R*S&&Zy*Fy'~=0.

On running it through Mat-lab, the optimized value of Zy and Fy comes out to be equal to zero,even though I have specified in the expressions that Fy and Zy matrices should not be equal to zero , because in my problem I have to use the inversion form of the matrices Fy and Zy .Each of the above defined matrices in the expression are all symmetric matrices of structure [2 1]

I don't know where I am wrong? Kindly help me and direct my problem to the right person.