# Redefining variables used in many equations in a publication

When using the same variables in many equations, should I redefine each time the variables and their meanings or is there other ways to avoid redundancy?

E.g.

c = a + b where a is...

z = a / b where a is...

It will maybe depend on the journal, but thanks for any general idea or opinion.

I think of this as a matter of "breadcrumbs." If a reader is constantly wondering what "a" is and having to look back to try to find its definition, that is a problem. On the other hand, if I put so much redundant definition in that the math gets hidden by uninteresting boilerplate prose, that's also a problem.

My preference is thus to take a two-pronged approach:

1. Create a table of symbols that collects all of the definitions in one easy-to-find location, and
2. Match every equation with a prose summary of its meaning.

For example, if I were presenting Newton's laws, then I might say:

"The force exerted by an object is proportional to mass and acceleration: F = ma."

and in the table of definitions "F" and "m" and "a" would all have their formal definitions. In this way, I remind the reader about the definitions without repeating them, yet at the same time have a simple reference point at which all definitions may be readily found.

• Your second part seems to only be useful when such an explanation is readable (I would certainly hate to try doing that for most of the equations I tend to write). Commented Nov 10, 2015 at 8:21
• @TobiasKildetoft For more complex equations, you can usually still put a summary of meaning, it will just be much more abstract. Commented Nov 10, 2015 at 12:46

Different authors use different notations and when making a litereture review it might get confusing if there is no explaination of the symbols whatsoever.

In general I would say that it helps if all symbols are explained once in the paper, at a centralized table or by their first appearance. Even if to you it may be redundant, please keep in mind that the reader is not necessarily familiar with your topic.