Suppose we set all the impedances which connect one grid point to another to be equal to some constant which is independent of position. Thus

We then choose, to satisfy (4.33) and (4.34),

and this leads to the conditions

where

The lower bounds on coincide when

in which case we have

Since in general, , for either even or odd, we are no longer at the optimal bound, and are forced to use a smaller time step than in the previous two cases, if we wish the network to remain concretely passive. This arrangement bears a strong resemblance to the MDWD network in [107] and [131], and discussed in §3.7. We will explore this similarity in more detail in §4.10. Many other choices are of the waveguide immittances satisfying (4.33) and (4.34) are of course possible.