# Computational domain discretization

In order to solve Maxwell's equations using the finite-difference time-domain method, the computational domain must be discretized.

The computational domain in FDTD++ is currently discretized using a Cartesian mesh with circulating electric and magnetic field components, known as the Yee cell[1]. See the image to the lower right.

Illustration of the Yee cell. JMM: This image shows a left-handed coordinate system -- it needs replacing.

## Controlling the discretization

The discretization is controlled entirely by setting the domain disc simulation parameter in the parameters file.

As an example, in order to change the discretization spacings along $x$, $y$, and $z$ to 2 nm (from their default values of 1 nm), the following could be added to the parameters file:  

 domain disc 2.0e-9 

or explicitly set the discretization along each direction:  

 domain disc 2.0e-9 x domain disc 2.0e-9 y domain disc 2.0e-9 z 

The latter case also demonstrates how one may modify the discretization along directions non-uniformly.

## Notes and references

1. K. S. Yee, "Numerical solution of initial boundary value problems involving Maxwell's equations in isotropic media," IEEE Trans. Antennas Propagat. 14, 302-307 (1966).