Why X and Y?

[viscousmemories]

I was just wondering...

People are always using X and Y in examples. Like:

"Say person X has desire Y..."

What's that about? Why not A and B?

Also, is this related to the X and Y axis business?

Apologies in advance for my lack of basic education. :wave:

[Dingfod]

I use P and U, multiplied they are PU, the stinkiest variables on the planet.

[Goliath]

I don't think there is any particular reason...the closest thing to a reason would probably be a mix of tradition and the fact that the letters "x" and "y" are oftentimes used to refer to real variables.

[Dingfod]

x is probably used because it appears fairly rarely in language and is distinct enough that it doesn't resemble any other letter. y just follows x alphabetically. I suppose z is often used in three-variable situations.

[Ensign Steve]

In beginner's algebra, I used A, B and C. But in pre-calculus we switched to X, Y and Z, with the x-axis going left/right, y-axis going up/down, and z-axis going front/back. Then in calculus Y changed to f(x) as in "Y=f(x)" or "the value of Y is a function of X." I don't know how Z fit into all that, because I dropped out of calculus pretty early. ;) But where did they come from? I dunno. I imagine that X was the original variable, because X is a cool way to represent The Unknown. But after that, your guess is as good as mine.

[viscousmemories]

Interesting.

Thanks y'all, I was sure there must be some obvious reason everyone but me knew.

[Shake]

Well, Goliath mentions tradition, which is a powerful force in society. I remember hearing once that usually x, y, z and other such letters near the end of the alphabet were typically used as variables, while letters near the start of the alphabet a, b, c, etc. typically denote constants -- whether known or not. Certain letters like i and e -- the square root of -1, and the exponential number 2.71828... respectively -- are reserved, or like t have other special meaning (t for time). Mathematics and physics use quite a few Greek letters as well.

But as far as using such letters in conversation, I'm not sure. It may have come from such conventions.

[viscousmemories]

Good points, Shake. Thanks. :yup:

[xorbie]

There are many traditions about these things in math. x, y and z are generally variables. I believe this started because X is used so infrequently, and Y and Z follow. i, j, k, l and are often used to denote things in a sequence, and written in subscript. n and m are generally integers, and used to count how many of something you have. a, b and c are used as co-efficients. pheta, and phi are often angles (I don't know if there's a way to type out the greek letters), epsilon and delta are generally small numbers, etc. etc.

I think it just helps to use similiar numbers although technically it is so arbitrary so as to make what you are doing easier to read through.

[xouper]

xorbie: ... i, j, k, l and are often used to denote things in a sequence, and written in subscript. n and m are generally integers,
This notion is also formalized in the FORTRAN programming language. If you don't declare your variable types, then any variable name beginning with i, j, k, l, m, or n was by default an integer type and all other variables were by default reals. An easy way to remember that rule was to recall the first two letters of the word "integer".

In the PHP or C programming language, for example, this is not formalized but the tradition has carried over from FORTRAN. Using i as an iteration counter almost goes without saying.





for (i=0; i<100; i++) {
document.write("xouper's a nut <br>\n");
}

[xorbie]

Indeed. That little bit with FORTRAN was actually rather annoying. I didn't know the language at all, but I had to rewrite a little computational algorith this summer. I tried to name a certain variable kr. Bad move.