====== cem ======

[{{ :cem_grating.jpg?230|Diffraction on a periodic grating}}]

Cem is a simple C implementation of the finite-difference time-domain method for solving Maxwell's equations. It can simulate and visualize a number of wave phenomena like diffraction or refraction.

===== Background =====

[{{ :cem_presentation.jpg?300|Me presenting at the contest. The text on the slide is a short description of FDTD. [[http://www.lo10.wroc.pl/pl/gala-finalowa-xii-edycji-otwartego-miedzyszkolnego-konkursu-fizycznego-im-bozeny-koronkiewicz.html|Source]]}}]

Written two years after [[ray]], cem got me the first place in the 12th edition of the "Open Interschool Physics Context" in 2015. The thing about this project I'm most proud of is how quickly I completed it.  It took me only two weeks to go from having never heard of FDTD to the finished program. 

===== Compiling and running =====

The source code is available at [[https://redman.xyz/git/cem|cem]]. While considerably more well-written than ray and even has a Makefile, your mileage may vary. 

This is a yet another program of mine with an arcane interface. The window displays a cross-section of the (cuboidal) simulation domain. Use the mouse to look around. Keys 1 through 3 switch between orthogonal cross-section planes. Keys 4 through 6 switch between different fields: the electric field, the magnetic field and relative permittivity. F3 opens a new window, so you can look at what's going on from different points of view.

Press return to open the command line. Try "load omkf/1.sim" or the other, bundled files. You can figure out the rest of the commands by looking at the .sim files. Press P and O to start and pause the simulation and press L to take a single step.