Voltage Dependent Resistor

Hello;

I want to simulate a simple electrical circuit as an initial step of my main study. In my study, I need to define the resistors whose values depend on the voltage gradient across them. However, Comsol give me the error "Circular variable dependency detected."

I know that this problem can be solved using conservation of charge in each circuit node and I have previously wrote a code to solve it. But, I do not know how to use Comsol to solve it.

Any suggestion will be highly appreciated.

Best Regards,
Andrew