Using the Contact Resistance model, one can effectively decouple the values of a given variable in two adjacent regions. In the previous example, if we replace the jump boundary condition with the statement
CONTACT(phi) = 0*JUMP(phi)
the contact resistance is infinite, and no flux can pass between the regions.
Note: The JUMP statement is recognized as a special form. Even though the apparent value of the right hand side here is zero, it is not removed by the arithmetic expression simplifier.