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February 2001 - Volume 4, Issue 2

IN THIS ISSUE

Letter from the Editor
Calculator News
MathTip: Derivatives of Inverse Functions
Interview with James Vernon
Miscellany

LETTER FROM THE EDITOR

Unfortunately, the start to ticalc.org's new year hasn't been as good as we expected. Our file archivers have fallen behind a bit, but we'll try to make up lost ground as soon as possible.

This month I've interviewed James Vernon, the Aussie who's programmed such stuff like Alien Breed: Tower Assault.

CALCULATOR NEWS

The most exciting news this month has been the announcement of a new TI-83+. This new calculator will run at 15 Mhz and have 1.5 megs of FLASH ROM. It'll be available in April or May, and will be silver colored! Find more information at http://www.ti.com/calc/docs/83psilver.htm.

In program updates, Sean Kelly has released The Incredible Adventure, a new side-scroller. Matthew Roberts released Coaster 83+, a 3D roller coaster program. Flavien Racien released a new BomberMaze68K, and Julien Muchembled released new versions of his TIB Receiver, MaxMem, and HW2Patch programs for the TI-89/92+ to work with the new ROM version 2.05.

That's about it for this month.

MATHTIP: DERIVATIVES OF INVERSE FUNCTIONS

Have any of you ever had trouble remembered what the derivative of arctan(x) or arcsin(x) were? Then this tip is for you.

There's a wonderful bit of math theory called the Inverse Function Theorem. Quoting from Serge Lang's Undergraduate Analysis, the theorem states:

"Let f be continuous on the interval [a,b] and assume a < b. Assume that f is differentiable on the open interval a < x < b, and that f'(x) > 0 on this interval. Then the inverse function g of f, defined on [a',b'], is differentiable on the interval a' < y < b', and g'(y) = 1/f'(x) = 1/f'(g(y))."

See the book for a formal proof. So using this in an example:

d(tan(x),x) = 1 + (tan x)^2

By the theorem we expect

d(arctan(x),x) = 1 / ( 1 + (tan (arctan x))^2 )
= 1 / ( 1 + x^2 )

Which is indeed the derivative of arctan(x).

So, before you reach for your TI-89 and hit the derivative key, give this theorem a try.

At ticalc.org, we often receive many of the same questions. In this column, we hope to address some of these questions for a broader audience. If you'd like to submit a question, please email it to ask@ticalc.org.

Q: How come assembly programs don't work on my HW2 calculator running AMS 2.05?

A: To fix this problem, download the recently-released HW2Patch v2.30 by Julien Muchembled, available in the ticalc.org archives. Install this program, and assembly programs will now be compatible with your calculator. Good luck!

INTERVIEW WITH JAMES VERNON

Email: jimbob_v@hotmail.com

Interview Log
 Eric How old are you and what level of education do you have? James I'm 18 (and a half), I've completed high school and I'm currently studying for an Advanced Diploma of Computer Science. Eric Where are you from? James I live in the state of Victoria in Australia, about 40 kilometres from Melbourne. Eric What do you plan to do after you graduate? James I'm not sure exactly, although I'm sure I'll be looking to work in the Artificial Intelligence/Gaming field of programming. Eric What calculators do you own? James An old TI-83 - v1.07 ;) Eric Do you plan to get any new calculators soon? James I might get a TI-86 later this year.. I wouldn't mind an 83+ but I'm pretty sure I'd prefer the 86. Eric What do you use your calculator for most? James When I'm at school I use it a fair bit for math, although these days it isn't as useful as it used to be mainly because the 83 doesn't have things like vectors or more advanced Calculus stuff. That's another reason I would like a TI-86. Other than that, I program for it. :D Eric What was the first program you ever wrote? James Hmm, don't everyone laugh - Guess a Number ;) I wrote it in BASIC the first day I got the calculator, and it was the first program I had ever attempted to program on any platform. That's pretty much how I got interested in programming. That would have been in about February 1998. Eric How did you learn to program in assembly language? James ASMGuru ;) Many thanks to James Matthews. Also I looked around and pretty much gathered information from many tutorials that people have written, such as Ahmed's journals. These days I still look for more information, now I use The Guide as I'm doing some TI-86 work. Eric Do you have an idol TI programmer? James There are heaps of guys I've admired for their work on TI calculators, most of all though I would have to say Bill Nagel in my early days, also Jimmy Mardell has done some really cool stuff (Sqrxz), and Linus Akesson has done a few nifty programs over the years, such as Stranded ;) Eric How do you like working at TCPA? James It's great! Dan Englender has been especially helpful with Tower Assault seeing as I don't have an 83+ and there was some restrictions on how big the game could be. He did a great deal in helping with that. He deserves a great bundle of credit for getting the 83+ version working. Jason Kovacs and the other guys there have been helpful and encouraging too, although come to think of it, I only know about 5-6 of the guys in the group.. Eric What projects are you working on now? James Hehe, too many! If I don't watch myself I could end up with 4 huge projects going at once. I don't want to say too much about my main project, but let me just say that ACZ's Zelda game inspired me to create an epic RPG for the 86, hopefully there should be a demo out late January to early Feb. Unlike many big 86 projects, this one should get finished ;) On the 83/83+, I'm slowly thinking about doing an R-Type sort of game, although with External levels. Also, due to high demand, I've started throwing around ideas for another Alien Breed with the smooth scrolling but with External levels. I'm not sure what calculators this will be for yet, most likely the TI-83/83+ and maybe the 86. Finally, there is a possibility that I might do the remaining 3 missions for the Thunderbirds game I did for the 83/83+ last year. This project would be for the TI-86. That pretty much sums it up. As you can see, these projects should pretty much fill up my year. Just quickly, many thanks indeed to all the people that have emailed me with encouragement and appreciation for my games over the last year or so. It's sort of good to know that ppl are enjoying the games that I put hours into :)

MISCELLANY

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