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 red bullet Viewing mpeg movie files
 red bullet Dealing with .tar and .gz files
 red bullet About the animations' colormapping
 red bullet Autoscaling vs. global scaling

 red bullet C-F90 floating point differences
 red bullet Sanity Savers & FDTD


 red bullet Viewing mpeg movie files: You can download a file to a directory on your machine, and then use whatever mpeg viewer you have to play it. Or you can set your browser to view them automatically. Here's how I did it on mine (Netscape):

Edit menu -> Preferences
In the popup box click the arrow next to Navigator to show the submenus
Choose Applications
Scroll down until you see MPEG Video, then click on whatever appears next to it under "handled by" and hit "edit"
Click on Application
Type in the command to activate your movie player, and hit the OK buttons
-- I used: mpeg_play -quiet -dither color %s

An important note: be sure that the movie player you use has its play all frames option set. Some mpeg players assume that the file includes audio, so they skip frames to keep up with the imaginary audio track. This will make ToyFDTD animations look jerky.


 red bullet Dealing with .tar and .gz files:The tar files each contain several files within them. If you have a tar file with a name ending in .tar, you use a command like

tar xvf filename.tar 

to un-tar it, which will give you a new directory named filename which will contain all the files included in the original tar file. You can now do whatever you want with them. 

If your tar file name ends in .tar.gz, that means it is compressed for faster downloading. To un-compress a your filename.tar.gz, use a command like

gunzip filename.tar.gz 
This will give you filename.tar which you can un-tar as just explained. The commands given here are Unix commands, if your computer uses a different operation system, you'll want to use the appropriate commands for your system. You can also configure your browser to unzip and un-tar automatically as explained above for playing mpegs.

More info & free software: http://www.gnu.org/software/gzip/gzip.html


 red bullet About the animations' colormapping (For most movies/images): The entire simulation region is outlined with a box. Red, orange, and yellow indicate positive values, with yellow representing the greatest intensities and red representing values near zero. Blue and green indicate negative values, with green representing the greatest intensities and blue representing values near zero. In some simulations, the most negative value is mapped to yellow, so a yellow spot in the middle of green represents the most negative point.

          This TEM pulse (on a parallel-plate guide) starts out as positive, but after striking a PEC termination is reflected back negative.


 red bullet Autoscaling vs. global scaling: Two kinds of color scaling are used. Autoscaling every timestep scales the field intensities in that timestep to the full range of color values. This means that dim timesteps will look as bright as intense ones, but the structure of the fields in the dim timesteps will show well. Autoscaling is used for each animation unless global scaling is specified for that animation. Global scaling over all timesteps scales the entire simulation as a whole. Dim timesteps will barely show anything visible, but you get a good idea of intensity variation over time.
           The following images demonstrate: both are taken from the same timestep of the same simulation:

          The image on the left is autoscaled to the values present in that timestep. The image on the right is globally scaled to the range of values for the whole simulation. Since the greatest intensities were present early in the simulation when a pulse stimulus was introduced, the image on the right is faint by comparison after the pulse has been smeared or stretched out by the transfer characteristic of the guide.

 Am I the only sane dot on this page? Contacting the perpetrators:  lemiller@borg.umn.edu

ToyFDTD home

 Colorbar from a ToyFDTD simulation