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Dear All

is a unit problem... I will give you a general picture, I hope you can help me

I have a coupled system of equations for charge and spin densities. Up to here everything is fine.
I solve it using the PDE coefficient form (a system of 4 equations, one for n and 3 for the spin)

Additionally I want to solve the charge current. In my case depends on n and S. then J(n,S)

The question is

How can I plot J with correct units?

What I'm doing is adding the charge current to my system of equations in the PDE coefficient form to solve all of them altogether; nevertheless, comsol 4.2a assign to all my variables the same units, I cannot choose a different unit to my last variables which are the components of the charge current.

Do you know how to define different units for each dependent variable...or give me another way of solving this?
I know that only with n and S as a system I can solve n and S, so I just need to put these solutions in the equation for J(n,S), how can I do it because adding them to the system of the PDE coefficient form destroy my units.

thanks for your help