The Flux/Source boundary condition adds a flux or source
g on the boundary:
The first equation describes this boundary condition for a Coefficient Form PDE, and the second term describes it for a General Form PDE. The g term may contain a general expression of the dependent variables. The
q coefficient simplifies the implementation of a
Robin boundary condition by including a term on the form
qu, where
u is the dependent variable.
Enter a value or expression for the value of the coefficient q in the corresponding field or fields. The default value is 0. It adds a term
qu to the boundary flux or source, which can represent absorption or impedance at the boundary.
or 