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Above the equal sign or below, I want to say "newton binom" to explain my transformations. I tried \underline and more commands but had no success.

Vincent
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user227847
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  • Can you not use the figure environment with a caption? – Plergux Oct 29 '20 at 09:31
  • Personally, I would write it on the same line, a little further on the right. – Bernard Oct 29 '20 at 10:16
  • have a look -- https://tex.stackexchange.com/questions/528218/how-to-write-the-definition-of-each-term-in-an-equation-with-pointing-arrows/528226#528226 -- and -- https://tex.stackexchange.com/questions/263480/undersetting-an-arrow-beneath-an-equation -- and -- https://tex.stackexchange.com/questions/526435/how-insert-a-text-on-middle-right-of-eqnarray/526439#526439 – js bibra Oct 29 '20 at 11:09
  • In the LyX toolbar there is a button that says "frame decorations". Look at the last two rows (the icons with empty boxes). – scottkosty Oct 29 '20 at 15:13

1 Answers1

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I see two main options to achieve what you ask.

  1. Use amsmath's \overset command to place text above the equal sign.
  2. Use \mathop to make the equal sign an operator which takes superscripts and subscripts above and below, and use those to place the words.

Here's an example of use of these two options, with a third example where I placed the words higher above the equation using an array environment, so it does not mess up with the horizontal alignment.

\documentclass{article}
\usepackage{mathtools}
\begin{document}
\noindent
With \verb|\overset|:
\[
(1 + 1)^{2n} \overset{\text{Newton binom}}{=} \sum_{i=1}^{2n} \binom{2n}{i} 1^{2n-i} 1^i
\]
With \verb|\mathop|:
\[
(1 + 1)^{2n} \mathrel{\mathop{=}^{\text{Newton}}_{\text{binom}}} \sum_{i=1}^{2n} \binom{2n}{i} 1^{2n-i} 1^i
\]
With an \verb|array| in \verb|\overset|:
\[
(1 + 1)^{2n} \overset{\mathclap{%
    \begin{array}{c} \scriptstyle\text{Newton binom} \\ \downarrow \end{array}%
}}{=} \sum_{i=1}^{2n} \binom{2n}{i} 1^{2n-i} 1^i
\]
\end{document}

However, I must say that none of these options looks very good to me. I think mathematical manipulations should always be explained in complete sentences, from which equations should be a part. I'd go for something like the following.

Vincent
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