  We investigate a multi-user multiple-input multiple-output interference
network in the presence of multiple reconfigurable intelligent surfaces (RISs).
The entire system is described by using a circuit-based model for the
transmitters, receivers, and RISs. This is obtained by leveraging the
electromagnetic tool of mutual impedances, which accounts for the signal
propagation and the mutual coupling among closely-spaced scattering elements.
An iterative and provably convergent optimization algorithm that maximizes the
sum-rate of RIS-assisted multi-user interference channels is introduced.
Numerical results show that the sum-rate is enhanced if the mutual coupling
among the elements of the RISs is accounted for at the optimization stage.
