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// SPDX-License-Identifier: CC-BY-SA-4.0
// Copyright © Paweł Redman
#import "/common.typ": post, static, img, link-self
#show: post.with(
title: "cem",
date: datetime(year: 2020, month: 8, day: 15),
)
#figure(
img(static("software/cem_grating.jpg")),
caption: [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
#figure(
img(static("software/cem_presentation.jpg")),
caption: [Me presenting at the contest. The text on the slide is a short description of FDTD. #link("http://www.lo10.wroc.pl/pl/gala-finalowa-xii-edycji-otwartego-miedzyszkolnego-konkursu-fizycznego-im-bozeny-koronkiewicz.html")[Source]],
)
Written two years after #link-self("software/ray")[ray], cem got me the first place in the 12th edition of the "Open Interschool Physics Contest" 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 #link("https://redman.xyz/git/cem")[cem]. While considerably more well-written than ray and even has a Makefile, your mileage may vary.
This is 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.
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