In order to show the TLM schema we will use time and space discretisation. The time-step will be denoted with Δ Δ t and the space discretisation intervals with Δ Δ x , Δ Δ y and Δ Δ z . The absolute time and space will therefore be t = k Δ Δ t , x = l Δ Δ x , y = m Δ Δ y , z = n Δ Δ z , where k = 0 , 1 , 2 , … … is the time instant and m , n , l are the cell coordinates. In case Δ Δ x = Δ Δ y = Δ Δ z the value Δ Δ l will be used, which is the lattice constant. In this case the following holds: