The Interior Source boundary condition can be used on interior boundaries only. With this node, the boundary condition is enforced according to:
where 
is the Lax-Friedrichs flux computed internally. Here the source g can be specified.
is the Lax-Friedrichs flux computed internally. Here the source g can be specified.Enter the flux term g (SI unit: 1/m). The default is 0 (1/m).