# Roman vs. Greek letters for variables

1. May 24, 2014

### oneamp

I am writing a paper and I was using 'o' for a variable. Then I decided that it looked too much like '0', and thought I might use capital omega. How do I know when I should and should not use Greek letters?

Thanks

2. May 24, 2014

What kind of paper? Different letters are used for different purposes.

3. May 24, 2014

### micromass

In principle, you could use any variable you want. Mathematically, everything is allowed. However, you should consider readibility. For example, using $\pi$ as a variable in equations is probably not the best idea. Or using $x$ as the function symbol and $f$ as variable to get stuff like $x(f) = f^2 + f + 1$ is also something you should want to avoid.

But it really depends on context.

4. May 24, 2014

### oneamp

Thank you. So it's arbitrary. Also, is using something like [smth]_{sub}, where sub is subscript, ok to use, or should I push the limit with unrelated (phonetically) roman and greek letters, instead of words with a subscript?

5. May 24, 2014

### micromass

Subscripts are perfectly fine. But again, it depends on the context. The end result should be a readable text, so notation shouldn't be confusing. That's the only rule.

6. May 24, 2014

### oneamp

I was more curious about using whole words above the subscript. Eg. $var_{now}$; can't $var$ be misinterpreted as three variables? Or is it ok to use it?

Thank you again

7. May 24, 2014

### micromass

It should be acceptable, but it's certainly something that you don't see very much.

In any case, use the text environment if you're using this. So

Code (Text):

\text{var}_\text{now}

To get $\text{var}_\text{now}$

8. May 24, 2014

### oneamp

Thank you

9. May 24, 2014

### symbolipoint

We have learned some unofficial conventions. f and sometimes g and h are often used for function names. Certain greek letters are often used as angle measure variables.

One maybe obvious reason for single-character variable names is that we place factors next to each other with the understanding that if no operation symbol is shown, then multiplication is understood. We can not try to spell human-language words with these kinds of variables. Why? Each letter is supposed to be a separate number.

10. May 24, 2014

### Lavabug

I've seen both in the literature but Greek letters are always more common, I think Roman letters are more typically used for dimensionless parameters like in numerical simulations or for geometric quantities (x,y,z, L etc.)

Plenty of Greek letters with Roman super/subscripts in papers, though the super/subscripts are almost universally in roman font instead of the default TeX font, something I was told by my senior year project advisor. Ie:

\Omega_{\rm{something}}

11. May 24, 2014

Staff Emeritus
It's not arbitrary. This is a form of communication, and you should pick your variable names to facilitate communication. For example, you could say that the area of a circle is $\pi^2 R$, where $\pi$ is the radius of the circle and $R$ is the ratio of a circle's circumference to its diameter. And you'd be technically right. But this would be a very confusing thing to say.

12. May 24, 2014

### lurflurf

Thanks. I am going to start doing that all the time, but I like to use functions and operators that act to the left and no parenthesis so I will write

$f\mathrm{x}=f^2 + f + 1 \\ f^2\mathrm{x}=f^4 + f^2 + 1 \\ \Xi\pi\sin\mathrm{d}=\Xi\pi\mathrm{d}(\Xi\pi\ \cos)=(\Xi \mathrm{d}\pi+\pi\mathrm{d} \Xi)(\Xi\pi\ \cos)$

looks great