Ex+2(k)-E(k)1H(k+1/2)-H”(k-1/2) △t Eo △x Hn(k+1/2)-H"(k+1/2 1Ex2(k+1)-Ex2(k) LX E -12 k-2 k-1 k+2 k-11/2k-1/2 k+l/2 k+11/2 k+2l/2 E n+In k-2 k k+1 k+2 Figure 1.1 Interleaving of the E and H fields in space and time in the FDTD formulation To calculate H,(k+ 1/ 2), for instance, the neighboring values of E, at k and k+I are nceded. Similarly, to calculate Er(k+ 1). the value of H, at k+1/2 and k+I 1/2 are needed( ) ( ) ( ) ( ) 1/2 1/2 0 1 1/ 2 1/ 2 n n n n x x y y k k k k t x  + − − + − − = −   E E H H ( ) ( ) ( ) ( ) 1 1/2 1/2 0 1/ 2 1/ 2 1 1 n n n n y y x x k k k k t x  + + + + − + + − = −   H H E E