reduce spacing above fraction bar in display mode

Question

I have the following code:

$$
\begin{Large}
\textbf{Volume = } \bm{{\dfrac{nhs^2}{12}}\Bigl(\!\csc\bigl({\tfrac{\pi}{n}}\bigr) + 2\cot\bigl({\tfrac{\pi}{n}}\bigr)\!\Bigr)}
\end{Large}
$$

Which generates:

Which is what I want except for the excessive vertical space between nh$s^2$ and the fraction bar. Does anyone know how to reduce this? Using \frac instead of \dfrac didn't help and I don't want to shrink the whole fraction by using \tfrac.

Answer 1

I don't think you want to move the numerator nearer to the fraction line: consider

\frac{nhs}{10}+\frac{g}{2}

that I'll represent in two ways, the one you're asking for and the standard one

Do you see the problem? The height of the numerators are inconsistent. Having a single fraction in the formula is irrelevant, in my opinion.

You can achieve the reduced spacing with

\frac{\raisebox{-0.4ex}{$\displaystyle nhs^2$}}{12}

if you really want to, but I'd not do it. And I'd probably follow Mico's suggestion to do

\frac{1}{12}nhs^2

Second problem with your code. You want to emphasize your equation, but is there any reason to use \Large size and boldface? Your equation is already displayed, this is sufficient to emphasize its importance. Maybe (but I'd not do it) boldface, but definitely not \Large. Anyway, none of the methods Mico suggest is good, I'm afraid.

\documentclass{article}
\usepackage{amsmath}
\usepackage{lipsum}% for context
\newenvironment{vardisplay}[1]{%
  % #1 contains the settings to apply
  $$% start a display
  \hspace{0pt}\begin{minipage}{\displaywidth}#1\noindent\ignorespaces
}{%
  \end{minipage}\hspace{1000pt minus 1fill}$$\ignorespacesafterend
}
\begin{document}
\lipsum[1][1-5]
\begin{equation}
\mathrm{Volume} =
  \frac{nhs^2}{12}
  \bigl(\csc\bigl(\tfrac{\pi}{n}\bigr) + 2\cot\bigl(\tfrac{\pi}{n}\bigr)\bigr)
\end{equation}
\lipsum[2][1-5]
\begin{vardisplay}{\boldmath}
\begin{equation}
\mathrm{Volume} =
  \frac{nhs^2}{12}
  \bigl(\csc\bigl(\tfrac{\pi}{n}\bigr) + 2\cot\bigl(\tfrac{\pi}{n}\bigr)\bigr)
\end{equation}
\end{vardisplay}
\lipsum[3][1-5]
\begin{vardisplay}{\boldmath\Large}
\begin{equation}
\mathrm{Volume} =
  \frac{nhs^2}{12}
  \bigl(\csc\bigl(\tfrac{\pi}{n}\bigr) + 2\cot\bigl(\tfrac{\pi}{n}\bigr)\bigr)
\end{equation}
\end{vardisplay}
\lipsum[4][1-5]
\end{document}

Seeing the formula in context and compared to the other realizations should convince you that the first one is better.

The same but with

\frac{1}{12}nhs^2

Answer 2

The following screenshot features three equations: (i) the OP's original version; (ii) a version that cleans up the OP's code (e.g., by getting rid of a number of unneeded pairs of curly braces) and uses \tfrac{1}{12} nhs^2 in place of \dfrac{nhs^2}{12} to achieve the OP's stated formatting objective; and (iii) a version of (ii) that employs normal-weight math, as I don't understand the purpose of bold-facing the entire formula. "For when everything is bold, nothing is bold..."

Aside: Please don't use $$ in a LaTeX document. Instead, use \[ and \] to initiate and terminate an unnumbered displayed math group. For a longer discussion of this issue, please see the posting Why is \[ ... \] preferable to $$ ... $$? Finally, do note that \Large is a text-mode command; its use inside math mode can have unpredictable results.

\documentclass{article}
\usepackage{amsmath,bm}
\begin{document}
$$
\begin{Large}
\textbf{Volume = } \bm{{\dfrac{nhs^2}{12}}\Bigl(!\csc\bigl({\tfrac{\pi}{n}}\bigr) + 2\cot\bigl({\tfrac{\pi}{n}}\bigr)!\Bigr)}
\end{Large}
$$
\begingroup % localize scope of next two instructions
\Large
\boldmath % <-- use \boldmath before entering math
[
\textbf{Volume} = 
  \tfrac{1}{12}, nhs^2
  \bigl( 
         \csc\tfrac{\pi}{n} 
      + 2\cot\tfrac{\pi}{n}
  \bigr) 
]
\endgroup
\begingroup
\Large
[
\mathrm{Volume} = 
  \tfrac{1}{12}, nhs^2
  \bigl(
         \csc\tfrac{\pi}{n} 
      + 2\cot\tfrac{\pi}{n}
  \bigr)
]
\endgroup
\end{document}