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FDTD finds the E/H fields directly everywhere in the computational ___domain. If the field values at some distance are desired, it is likely that this distance will force the computational ___domain to be excessively large. Far-field extensions are available for FDTD, but require some amount of postprocessing.
Since FDTD simulations calculate the E and H fields at all points within the computational ___domain, the computational ___domain must be finite to permit its residence in the computer memory. In many cases this is achieved by inserting artificial boundaries into the simulation space. Care must be taken to minimize errors introduced by such boundaries. There are a number of available highly effective absorbing boundary conditions (ABCs) to simulate an infinite unbounded computational ___domain. Most modern FDTD implementations instead use a special absorbing "material", called a [[perfectly matched layer]] (PML) to implement absorbing boundaries.
Because FDTD is solved by propagating the fields forward in the time ___domain, the electromagnetic time response of the medium must be modeled explicitly. For an arbitrary response, this involves a computationally expensive time convolution, although in most cases the time response of the medium (or [[Dispersion (optics)]]) can be adequately and simply modeled using either the recursive convolution (RC) technique, the auxiliary differential equation (ADE) technique, or the Z-transform technique. An alternative way of solving [[Maxwell's equations]] that can treat arbitrary dispersion easily is the Pseudospectral Spatial-Domain method (PSSD), which instead propagates the fields forward in space.
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