### New Rules

Really a new rule: I have to publish a post every week that doesn’t consist entirely of links. Reading is a lot easier than writing, and there sure is a lot of great stuff out there … so my instinct is to just go on browsing and report on some of the highlights. And I mean to go right on doing quite a bit of that.

But there also oughta be something original from time to time. (Old joke. Consultant: Thanks for bringing me to your institution. You’ve got a great thing going here. All you need now is a Mission Statement, a Work Plan, and a Blogfor. Employer: What’s a blogfor? Consultant: A blog is for spouting your opinions and hoping for an audience. Dah-dum!)

So today, while I’m building up steam for yet another anti-graphing-calculator piece, I’ll share a few lines of code for the TI-*: the “integral checker” (INTCHECK).
$1 \rightarrow I$
$While I<8$
$nDeriv( Y_1(X), X, I) \rightarrow L_1(I)$
$Y_2(I) \rightarrow L_2(I)$
$I+1 \rightarrow I$
$End$
Put your (tentative) solution in $Y_1$ and your integrand in $Y_2$; run program INTCHECK; look at the “lists” that the program has generated (these are kept in the STAT menu); if all has gone well, you’ll see seven matched pairs: the derivative of your solution equals the integrand (for $X \in \{1, 2, 3, ... , 7\}$). Of course this isn’t a proof (it’s merely very convincing). Worse than that, the set in question might very well not even be a subset of the domain of our functions (consider $\int \sqrt{x-8} dx$). But it’s been useful to me just the same: if there’s been a mistake, this’ll usually find it out.

Anyhow, my students have been required to buy these doggone things, so when I can find out any actual use for one of ’em, I’m pleased to share it. In particular, I like showing off the programming feature: these silly little boxes are hand-held computers, not mere calculators. In fact, a TI is more of a computer to me than the PC clone on my desk in at least one way, since I’m not up to speed on any of the programming features of the latter (I’m convinced that Microsloth clobbered BASIC so people wouldn’t learn how easy programming is …).

OK, that’s enough out of me. Back to reading everybody else’s stuff.