Thank you, David Fink, for the answer.
Yes, I can use three different blocks, one for each equation but then I get three different answers. I want a single answer that satisfies the three equations at the maximum possibility. If you think of least squares formulation, I have
y1 = A1 * x
y2 = A2 * x
y3 = A3 * x
and I want to get the x that minimizes
|([y1_m,y2_m,y3_m] - [(A1 * x) , (A2 * x)), (A3 * x)])|^2
where yi_m is the ith measured output.
One option that comes to my mind is dimension reduction using eigenvalues. However, I don't know how to do that exactly.
Please let me know if you have any hints or suggestions.