Interpretation of the Time-Domain KW Converter
As shown above, driving a single displacement sample 
in the
FDTD corresponds to driving a velocity input at position 
on two
alternating subgrids over time. Therefore, the filter
acts as the filter
on either subgrid alone--a
first-order difference. Since displacement is being simulated, velocity
inputs must be numerically integrated. The first-order difference can
be seen as canceling this integration, thereby converting a velocity
input to a displacement input, as in Eq.
(E.23).
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FDTD State Space Model
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Additive Inputs
