Help with circuit simulation (Variable resistor/state space block)

Hello!

I'm trying to model a simple circuit with state-space associated with a variable resistor, but I can't generate any kind of signal (in or out). The main idea is found below, while the current through both resistors are changing, the value of variable is changing too. I have assumed that the minimum value of this is 0. Do I need to do something with those signals (current in and signal out, that is going to change the value of R)?

Thanks in advance!

PS: I'm working on 19b.