Hello, This is the first time I'm using COMSOL on a problem where I have multiple subdomains within the domain. Previously, I have only been using one domain/one set of equations/Two global sets of BC's. I've been having a hard time thinking of a solution to my problem. I have 3 subdomains, and all have their own set of ODE's and BC's. (They're really PDE's, but I'm going to assume stead-state for the time-being until I get it to work. I want to see the steady state solutions anyway as well.) The problem comes in that in the first and third subdomains, I have 3 equations each to solve. In the middle subdomain, I have 7 equations to solve. They are all heavily coupled, but the system is homogeneous and linear. So I have a total of 13 dependent variables. Is there a way to either: - Use overlapping subdomains so that I can have 3 subdomains in the middle rather than just one? - Have the first and third subdomains have a model for 3 equations each, and the middle one have a model for 7 equations? Because I can't do all 13 at once, as that gives me singular matrices during the finite element assembly. I am currently using a 1D PDE stationary model in the coefficient form with all the transient term coefficients set to 0 for the time being.