# Order N

## Summary

Recent work has discretised Maxwell's equations for implementation in an
Order N electromagnetism program via a Finite Difference Time Domain scheme.
The program is written in Fortran 90. At the moment the code can perform two
basic types of calculation.

The first is a band structure calculation, which starts off with an
arbitrary set of initial fields corresponding to some wavevector *k*,
integrates in time storing the fields at some random sampling points and then
Fourier transforms into the frequency domain. The peaks in the frequency
spectrum correspond to the frequencies the the allowed modes.

The second type of calculation finds the time dependent Green's function by
setting the initial fields to be a delta function in space for one of the field
components, zero for all the others. The fields are integrated in time and
stored at each time step to give *g(t,***r**,**r**'). Fourier
transforming gives *G(omega,***r**,**r**').

## Documentation and Source Code

Documentation is available in PostScript
format, or download the LaTeX documentation files, `onyx_doc.tar.gz`
or `onyx_doc.zip`.
If you do not have software to read PostScript files, the GhostScript Hompage provides, or
provides links to, software and documentation for most operating systems. The
source code is freely available in either a `.tar.gz` or `.zip`
archive.

last updated Mon 1 March 2004