VPAsolve with measurement error

Hello everybody

I have a question. I have to found a complexe number from an equation and the result of an experiment.

I have the measuremment of E, E0. k is a frequency vector, d the thickness of the sample used.

!! E, E0, n are complexe!!

I solve it with with a vpasolve in a for loop, Ratio = E/E0

for kk=:length(k)
syms x y

A =(4.*(x+i*y));
B= 1+(x+i*y)  ;
C=exp(i.*k(kk) .*d ;
eqn=(A)./B.*C;
eqn1= real(eqn)== real(Ratio(p));
eqn2= imag(eqn)== -imag(Ratio(p));

varLimits = [0.1 10; 0 4];

S = vpasolve([eqn1 eqn2 ],x,y,varLimits);

end

It's working really well, BUT, d is not perfectly defined, at 10%, that gives me a huge range of x and y.

How can I add this error during the solving?

The derivation of my equation with d?

but I have no idea how to do something with this

Regards