After discretizing the conservation equation, there is an equation for
every cell in the problem, but roughly three extra unknowns per cell have
been added. Closure is achieved by applying a continuity of flux condition
at each cell face:

where *c*1 and *c*2 are the two cells that share the face *f*. If, for example,
face *f* is a - *m* face in *c*1 and is a + *k* face in *c*2, this equation can
be written out as

The 11-point stencil for the cell face equations is shown in Figure 6.