How to use y2abcd function if y parameter matrix has variables

I have to find the equivalent of three two port networks cascaded as below where x1 and x2 are variables ans the matrices represent y-parameters. I am trying to convert them to abcd matrix and then multiply to obtain equivalent abcd which can then be coverted to y.

This is the code I have written for the same

syms x1
y1 = [x1,-x1;-x1,x1];
syms x3
y3 = [x3,-x3;-x3,x3];
syms x1
t1 = y2abcd(y1);
syms x2
t3 = y2abcd(y3);

But, I am getting an error

Answer 1

[Walter Roberson]

Nothing in the RF toolbox accepts symbolic parameters (unless it is by accident.)

You cannot use y2abcd() with symbolic parameters.

That said, the calculation is:

syms x1
y_params = [x1,-x1;-x1,x1];
abcd_params = [
        -y_params(2,1).\y_params(2,2), -1./y_params(2,1);
        y_params(1,2)-y_params(1,1)./y_params(2,1).*y_params(2,2), ...
        -y_params(1,1)./y_params(2,1)];
disp(char(abcd_params))

[1, 1/x1; 0, 1]