Signal flow graph, describing a RC circuit? Hi, guys. This is my first post on this forum! I'm trying to understand this example in my textbook. The current and voltage equations are: where G=1/R, Z(s)=1/Cs, and I1(s)=I1 Then the text says the following signal flow graph can be obtained: And finally we can somehow obtain the transfer function: First question, why is it necessary to do the substitution for G, Z(s) and I1? For the fourth equation, it says V3=I2Z, where Z(s)=1/Cs. Therefore, V3=I2/Cs (voltage=current/capacitance)? Where does this relationship comes from? Lastly, how do I know how many equations do I need? And which circuit elements should I describe? I might have more questions later, but I couldn't proceed without know the basics. Thank you so much!