Returning to Figure 3.14(a), and making use of the discrete two-port derived in the last section, we can now write the complete wave digital network. It is shown in Figure 3.14(b).

The inductances in the MDKC of Figure 3.14(a) are

and the port resistances of the MDWD network of Figure 3.14(b) are

The MDWD network is MD-passive if all the port resistances are non-negative over the entire spatial domain; from (3.63) and (3.64), the only port resistances which are possibly negative are and . Requiring their positivity gives the constraints

where and . A judicious choice of [131] allows the largest possible time step for a given grid spacing; the condition is then

where is defined by (3.59).

If and are constant, and (3.65) holds with equality, so that we have

(3.62) |

then the MDWD numerical scheme is said to be operating at the