lardbucket: math


Calcsy – See your calculator on your computer

Filed under: Education, Math, Programming, School, Technology — aschmitz @ 9:17 pm

Calcsy LogoCalcsy is a tool you can download and use on your computer to show (and save) the screen of your TI-84+ or TI-89 Titanium calculator.

It’s useful for projecting the screen large enough for other people to see, or for taking a screenshot to use in instructions. For example, I’ve used it in teaching how to graph functions on a calculator, and I suspect it will be similarly useful to other people.

I first wrote Calcsy almost two years ago, and have been (very) slowly making it better since then. It’s now to a state where I think it’s reasonable to release. At the moment, it’s only available for Mac OS X, although it should be possible to port to Windows if there’s enough demand. Hopefully it’s pretty self-explanatory, but feel free to let me know if you have any questions.

All you need is a TI-84+ (or TI-84+ Silver Edition) or TI-89 Titanium and a USB cable to plug it in to your computer. The program is free, and you don’t need any special software on your calculator. (You also don’t need one of the special “Presentation Link” adapters – your computer and a normal USB cable works just fine.)

Other details of note: I suspect it won’t work with the very new TI-84+ Color calculators, but I’m happy to try to make it work if someone wants to send me one. Also, the logo was made by David Felice, so thanks are due to him.

Anyway, it’s free, go check it out. Let me know if you have any questions/comments/problems/etc.

Andy Schmitz



Filed under: Ego, Math — aschmitz @ 11:29 pm

A number of you who know me in real life have probably seen a number of my posters. Three of them currently adorn my dorm room. I had been offering them to friends I knew, but not to everyone, because I hadn’t gotten around to it. But that has changed now, with

The website itself is (purposely) a bit sparse, but it will let you browse the four existing posters, and grab one for yourself from Zazzle at fairly reasonable prices. (I really only make a few dollars from each one, depending on size.) Other than taking a while to ship, Zazzle’s processing has been fairly good, and the three large prints I have from them are reasonably high quality, even on their “basic poster” paper.

Each of the posters on was created by me, using a reasonably high-powered computer to do the rendering. Each of the posters is a mathematically-defined rendering, and could theoretically be rendered at any size and not lose any detail. Therefore, the large posters are still high quality images.

So, if you’d like to get a neat-looking poster and send a few dollars my way at the same time, have a look at

Andy Schmitz


Mathy Bits

Filed under: Math — aschmitz @ 11:21 pm

So, it looks like there’s a surprising amount of noteworthy stuff going on in the cryptography community at the moment.

First, Bruce Schneier points out a paper from Dan Shumow and Niels Ferguson (PDF warning) (at CRYPTO 2007) that indicates it’s possible that the NSA (or the NIST, or someone) has inserted a backdoor in a newly standardized random-number generator that makes it possible to predict its output. (Actually, to know its output, if I’m understanding correctly.) That means that any randomness used for cryptography is completely useless if someone knows the secret numbers, which is at least plausible. In short, don’t use “Dual_EC_DRBG”. Or, if you absolutely have to, change the constants.

Then, Adi Shamir notes that a single unknown flaw in a math processor on a CPU could also break important parts of cryptography if someone finds out about it (and is able to preform a known-plaintext chosen-plaintext attack). Of course, he’s not saying one exists, and I’m not sure why that came out now as opposed to any other time, but it’s interesting nonetheless.

Speaking of Adi Shamir, I’m pretty thoroughly convinced that tossing the modular arithmetic into Shamir’s secret sharing algorithm the way it was intended will give proper, non-leaking results. It looks like the flaw is really just an implementation flaw in the way I was looking at the problem (and the way it was replicated on the Wikipedia). So, while it’s something to look out for if you’re actually implementing the algorithm, it’s not a major problem if you’ve got a working, proper implementation. I’ll try to update my blog post (and the affected Wikipedia article, if it still needs fixing) soon.

Andy Schmitz


A Flaw in Shamir’s Secret Sharing method?

Filed under: Math — aschmitz @ 1:36 pm

(This post is going to be much more mathy than my standard posts, mostly because I thought about this as I was filling out college applications and decided it would be interesting to follow up on the random thought.)

(I apologize in advance for the poor quality \LaTeX renderings, but they should at least be legible)

A bunch of math follows in the full post.


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