Hi!

Wow, lots of new stuff this month for TI calculators. More about that in the Calculator News section of this newsletter. Behind the scenes here at ticalc.org, we've updated our news system so that comment pages are split into parts as they grow large, for users with slower connections. We're currently working on options to allow users specify the number of comments to display at once.

The Program of the Month awards will start up again on ticalc.org. Programs will be selected in four categories: TI-82/TI-83/TI-83+, TI-85/TI-86, TI-89/TI-92/TI-92+, and Computer Utilities/Miscellaneous Programs. All programs released this month that are designated as Featured Programs will be eligible.

This month I've interviewed Steve Whittaker, our local ticalc.org File Archives maintainer.

Thanks for reading the ticalc.org Newsletter!

Eric Sun

As I mentioned before, this was an extremely eventful month in the TI world. First, yet another rom version for the TI-89 and TI-92+, AMS v2.05, was released. You can find more information at http://www.ticalc.org/archives/news/articles/3/38/38694.html.

Many notable programs were also released this month. Probably the most exciting was the release of MirageOS, a new FLASH shell for the TI-83+ created by Detached Solutions. This shell has a huge number of interesting features that we've never seen before on any calculator. Find more information at http://www.ticalc.org/archives/news/articles/3/38/38832.html or visit their web page at http://www.detacheds.com/.

The Doors Team has also released the new version of DoorsOS II. The new version contains some bugfixes and new features. Download it from our archives or visit their home page at http://doors.ticalc.org/.

Until next time...

Eric Sun

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: I'm worried about the new MirageOS shell writing to the FLASH memory on my TI-83+.

A: MirageOS should be perfectly harmless. As Dan Englender, member of Detached Solutions and one of the chief programmers of MirageOS, said, "We were very conscious about keeping FLASH writes as low as possible, so the only time the the AppVar is written to is the first time you run the application, and when you change options (and it's not even when you change an individual option, it's when you quit the options screen, *if* you've changed any options, that it's rewritten). In addition to that fact, we added an option to MirageOS to allow those of you worried about your FLASH to keep writes to FLASH at near zero. If you go to Miscellaneous Options and uncheck the "Allow Write-Back In Archived Progs" option, no programs will be rewritten to your archive. If you do this, high scores will not be saved in archived programs, but it will *greatly* reduce the number of writes to FLASH, and speed up loading and unloading time." According to TI, it takes about 100,000 erasures of the FLASH memory for the FLASH to wear out. So, you most likely have nothing to worry about running MirageOS on your TI-83+.

Eric Sun

Solving systems of equations is a common task that you are often asked to do in math classes. Usually, the most focus is placed on linear systems of equations. You will undoubtedly be subjected to many techniques that are tedious paper-and-pencil methods. If you have the privilege of using a calculator on a test or homework, you may have wondered if there is an easier way. Indeed, teachers often save calculator methods for the end of the chapter. They also often choose the most inefficient way to do it on the calculator: writing a product equation for the system and solving by computing the inverse. Fortunately for us, the calculator has a much simpler way, rref(). rref stands for Reduced-Row-Echelon-Format. It takes a augmented matrix as its argument. What is an augmented matrix? Well suppose you had a linear system consisting of the equations:

/ 3x + 4y + 2z = 1
| 2x + y + 3z = 0
\ 5x + 4y - 2z = 1

then the augmented matrix would look like:

/ 3 4 2 1 \
| 2 1 3 0 |
\ 5 4 -2 1 /

The solution to this system will be x=a, y=b, z=c where a,b,c are constants to be determined. We often write the solution as an ordered triplet (a,b,c) (or ordered pair in the 2 dimensional case).

To solve this system, we would type the command:

rref([[3,4,2,1][2,1,3,0][5,4,-2,1]]) into our TI calculator, and it would display:

/ 1 0 0 -1/10 \
| 0 1 0 7/20 |
\ 0 0 1 -1/20 /
(the fractions would be decimals if it was not done on TI-89 or TI-92/+)

So our answer is x=-1/10, y=7/20, z=-1/20.

Andy Selle