# What label to use in an article for a group of equations?

Writing an academic paper, one might use different labels for different entities. For example in MS Word, Figure, Table, and Equation might be used for figures, tables, and math equations, respectively. Equation labels are typically placed to the right side of the equation. What label should I use for a group of equations? Can I use equations (for example equations (15))?

Update:
Here is an example group of equations from a mechanics-related text, where different parameters of a criterion are calculated in a series of equations. what do we call such a group as a label (e.g. [label] 7)?

In this study, Mohr-Coulomb criterion has been selected in this study as the fracture criterion. Parameters of this criterion are calculated corresponding to [label]s(?) 7 to 9.

• Thanks for the update. This is a good question; I hope we can provide an answer. – Monica Cellio Jan 12 '15 at 15:24
• Is there a reason why you can't say "Equations 7 to 9"? As long as each one has an identifying label, what's wrong with using "equation"? – Lauren-Clear-Monica-Ipsum Jan 12 '15 at 16:55
• @Lauren that's because it is a group of equations not one equation. – codezombie Jan 12 '15 at 17:28

A common way to number a group of equations is to use a single number for the whole group and lower-case letters to identify the different equations (subequations). For example, the above equations can be numbered (7a), (7b), (7c) and (7d). You can then refer to each single equation (e.g. "Equation (7a) yields...") or to the whole group (e.g. "The set of equations (7) represents..."). The choice depends on your needs. In the example you provided, probably, the author did not need to refer specifically to any of the subequations.

If you are using LaTeX to typeset your document, the amsmath package defines the subequations environment for this purpose.

What you might want to do is:

1. Decide (by refering to relevant literature) if your formulas are considered (a) one equation with a set of subequations, or (b) a series of equations.

2. If they are one equation with subequations, label each subequation consecutively with letters: 1a, 1b, 1c, etc. If they are a series of equations, label each equation consecutively with numbers: 1, 2, 3, etc.

Always label each (sub)equation! Do not give one number for a group of equations as you did in your example.

Your three options are:

All of these three are common in published articles.

3. In text, refer to a series of equations as "equations 1 to 4", to an equation with subequations as "equation 1", and to an individual subequation as "subequation 1b".

Assuming that the equations have a relationship (such as all describing different properties of the same process) they are a set of equations, but the question is are they a named set? If they are a named set, use their name, otherwise you should label them.

• What do you mean by a named set? And how do I label then if they aren't? – codezombie Jan 12 '15 at 22:37
• I guess that hildred means that certain mathematical equations or procedures have names, usually after the person who invented them or the purpose they are used for. – user5645 Jan 13 '15 at 7:58