Math/programming question

[dragonflame]

So I had this math class today and I have a question about graphing calculators.

I'm using one of these:
http://upload.wikimedia.org/wikipedia/commons/2/2d/TI-84_Plus_graphing.jpg
(Warning, huge image)

Now these things have a lot of calculating options etc (IE: defining the exponent of powers and roots etc, so you can perform more calculations than with just square powers and square roots) but somehow the only logarithmic option is 10log(X) (or log10(X)) (The common logarithm) <- the base being 10.

We have to manually put in 10log(X)/10log(Y) in order to perform Ylog(X). Now to me, this seems pretty simple to program. A lot of advanced calculations are programmed into the calculator but defining the base of your logarithm is not.

Why?

(Google isn't giving me any answers, and my math teacher doesn't know either)[/img]

[Namhias]

I'm familiar with that model, I use it all the time.
There are two logarithmic functions on that one, Ln (elog) and Log (10log). There are simply no additional ones needed as these two are the most common. If you'd like to calculate something different from that, you'll have to use your earlier mentioned notation.

a "ylog" button wasn't present in the previous versions either, probably because it wasn't needed, or because there was not enough space for an additional button.

I could write a program for it if you'd like. Like you said, it's not difficult. I don't have the time to do it now, but if you're curious, I could give you the syntax.

[dragonflame]

Thanks Namhias, send me the program if you wish to.

The actual thing I would like answered is not IF there isn't another button to specify the base or HOW to do it but rather WHY the original programmers didn't include a button for it.

[Namhias]

My best guess would be that the original designers didn't deem it necessary.

[Hyraxylos]

I used to remember how to use logarithms and I keep forgetting what numbers go where to do what. I think I should keep it written on a note or maybe a t-shirt or something.
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[Ragnarok]

Because for all practical purposes, you only really need base 10 and base e... and really, base 10 starts being less useful after a while. I think the last time I really had a base 10 problem was back in high school, or maybe back when I was in calc... everything I can think of that's related to my current program (transportation engineering/civil engineering) was base e.

And the last time I had a log that wasn't base 10 or base e, was back when I was learning logs, when they try to drill all the properties into your head, whether you need them or not.
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[Namhias]

In my field (applied physics), it's actually the reverse. Most of the theoretical equations are base e, but in practice, we use base 10. We have a lot more practical problems to deal with, and less so with the theoretical ones. I never use any of the other ones.

...Which reminds me that I still have to give you that code... I'll get to it soon.

[Ragnarok]

It's been a while since I used a lower 80s series TI (using an 89 now), but I think the code is something like:

display: "B log(A)"
display: "B?"
Input B
display: "A?"
Input A
log(A)/log(B)

...and I think that should spit it out... or the last line might need another "display" in front of it or something, but that should be pretty close.

Of course, it'd probably be faster to remember logA/logB than to have to run the program every time...