============================================================== | | | readme.txt - by Don Cross | | | ============================================================== The file FFT.ZIP contains C source code for performing Discrete Fast Fourier Transforms (DFFTs) and inverse DFFTs. This source code is public domain. Use at your own risk. For more information, point your web browser at: http://www.intersrv.com/~dcross/fft.html Also, feel free to send questions/comments about this source code to me by e-mail at the address above. ------------------------------------------------------------------------------ *** IMPORTANT NOTE *** There are two different ways to define the FFT (and inverse FFT) that result in having the same outputs, only the imaginary parts are negated. In other words, the two different algorithms produce results that are complex conjugates of each other. The popular mathematical software tool MATLAB and my FFT source routines use opposite definitions. However, it is easy to make my FFT source code compatible with MATLAB. To do this, use your favorite text editor to change the following files: fourierd.c fourierf.c Look for the line of text that says: double angle_numerator = 2.0 * DDC_PI; And change it to: double angle_numerator = -2.0 * DDC_PI; That is, just make the angle numerator negative instead of positive. Be sure to do this in both fourierd.c AND fourierf.c so you have consistent routines for both single- and double-precision math. I am considering changing my code to be compatible with MATLAB, but first I would like to find out if there is some definitely "correct" or "preferred" definition within the mathematical community. If you have any comments on this issue, please let me know at the following email address, because I'm stumped and need help! dcross@intersrv.com Thanks! ------------------------------------------------------------------------------ *** SMALL REQUESTS **** If you want to give away copies of this source code, that's fine, so long as you do the following: - Do not charge any money for this source code, except for possibly a reasonable fee to cover postage, disk duplication, etc. I wrote this code and I want it to be FREE to EVERYONE! - Do not remove my name, e-mail address, or URL from any of the files in this collection. - Please keep this readme.txt file with the source and headers so that others can get in touch with me to ask questions and/or find my web page to read the online tutorial. - If you make any modifications to the source code, please add comments to it which include your name, e-mail address, web page URL (if any), and explain what you did to the code. - If you use this source code in an interesting program, please let me know. I promise will never try to get money from you, even if you use this code in a commercial program. I just want to know what kind of clever and creative things people do with Fourier Transforms.