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When I have equations, as in

\begin{equation} ... \end{equation}

Can I arbitrarily assign the numbers to the equations? Instead of the usual order (1), (2), (3), ..., I'd like something like (1), (2.1), (2.2), (2.3), (3.1), (3.2), (4), ...

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Is there some logic behind the numbering, or is it purely arbitrary? – Werner Feb 8 '13 at 3:56
@Werner Thanks for your question. They are the equations under Theorem 1, Theorem 2, and so on. Is there a convenient way to do the numbering? – Paul S. Feb 8 '13 at 4:06
@PaulS. see my update :) – cmhughes Feb 8 '13 at 4:11
up vote 9 down vote accepted

Yes, absolutely, using the amsmath package and its \tag command.

A little example




After reading your comment, if you want the equation number to inherit the theorem number, then you can use, for example,


and then you don't have to tag equations manually.

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Yes, thank you! – Paul S. Feb 8 '13 at 4:06

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