Current version: 1.4b (beta), released 4/27/2001.
Mac Brownian Motion is a program that simulates (tah dah...) Brownian Motion. Brownian Motion is exhibited in a variety of situations, including motion of particles. Much of stochastic analysis (introduced in a graduate statistics program) is based on the properties of Brownian Motion. Physicists, engineers, economists, and statisticians all rely on its nice properties.
It is primarily an educational tool. In fact, its purpose is (originally) rather narrow: to visualize Brownian Motion in one dimension over time. I created the program because for the longest time, I worked with Brownian Motion and did not really understand what it looked like. Now that I’ve written this program, I do. I’ve released it so that others may benefit, too. Throughout the updates, I added some other types of simulations (so that I could see them), improved random number generation, and reorganized to make the interface a little more intuitive.
I hope this will make Brownian Motion, which lies at the heart of a lot of scientific and economic modeling, a little more accessible to people who have not the time or the patience to learn the nuts and bolts of stochastic analysis. And to those who are trying to learn stochastic calculus.
The Windows version requires Win 95 or better. (Yes, Mac users, I know the joke.)
The Mac version requires 8.6 or higher with CarbonLib, or OS X.
Hardware requirements: those that will run the OSes listed above. Quicktime will allow saving to different formats other than PICT (Mac) or BMP (Windows). The faster processor and more memory you have, the better. I'd recommend at least 10 MB if you want to go crazy with this. You may be able to get away with 4 MB.
The Mac version requires Stuffit Expander 5 or greater (get here) to decompress. The Windows version requires any unzipper (such as WinZip).
Using Mac Brownian Motion
A saved file of Mac Brownian Motion
[ Mac Carbon | Windows | Thrillseekers' version (Mac Carbon only) ]
I’ll listen to user feedback, including feature requests and bug reports (please consult below before sending a bug report).
Fractional Brownian motion was pulled because the algorithm I was using had a bug somewhere that is a devil to track down. I didn't want to lead you astray, so I pulled it temporarily.
Serious cosmetic issues were making resizing a pain. I had it worked out so the graph would recenter when you made the graph larger. If you cleared the graph after a resize, that worked as well. But if you made the window smaller than the current graph, part of the graph would be eaten. Ugh. So I killed resizing for the moment.
Windows doesn't support custom colors. That is because REALBasic doesn't support custom colors for Windows. The option is there, but if you try it you'll get a small reminder. I can't clear this up until RB adds support, or I write a custom colorpicker class. I doubt the latter will happen.
Undo is still a devil. The code is there. It gets executed. But the undo doesn't happen.
The ‘thrillseekers' version’ (really 1.4d1) also has lightly-tested EPS export features and ‘correct’ resizing of the window. It also takes up a lot more memory.
1.4b was released on 4/27/2001. Again another year's lag. Well, I got Mac OS X and REALBasic 3.1, and I'm trying to get back into programming. So what a good way to start—update a program. Well, while this version looks like a step backward, it is not. I've temporarily removed some features that were causing really annoying problems. I've also removed non-portable code so that I can cross-compile. In addition, I made it easy to contact me (pull up the about window) and changed the default values to something that will look pretty good.
v1.3b2 was released on 5/8/2000. This is because it took me a while, between dissertation, work, and sleeping, to figure out how to implement FFT in RB. FFT is needed to implement Fractional Brownian Motion (yes, I had an implementation before, but it was wrong). I also implemented tooltips. 4/27/2001: I've discovered much to my chagrin that, in fact, the collection of pixels the algorithm spewed forth was not FBM.
v1.3b1 was released on 3/1/99. All I really did here was add Fractional Brownian Motion and brought back refreshing for a resized window. If this causes problems, email me. (*NOTE: the implementation of Fractional Brownian Motion in this version is wrong!)
v1.2 was released shortly after v1.1, mainly to remove some features that were wreaking havoc. In specific, undo was removed, as well as updating the graph after a window resize. I also added 2-dimensional Brownian Motion and the Brownian Sheet.
v1.1 was released on 2/7/99. It features some improvements to the interface, including a more organized set of controls, a more "Mac-like" look-and-feel, some undo, improvements to random number generation, and the addition of reflected brownian motion. See the readme for more details.
Also, I check for Mac Shareware updates at Versiontracker.