# How do I make my nicefrac fraction line larger?

I am trying to replicate this formula with LaTeX:

However, I am struggling to make the fraction look the same. This is my attempt:

$$\label{eq:alphaK} \alpha(k) = \frac{1}{(N-k)} \nicefrac{ \left( \displaystyle \sum_{i=k+1}^{N} \lambda_i \right) }{\left( \displaystyle \prod_{i=k+1}^N \lambda_i \right)^{\frac{1}{N-k}}}$$


Which results in the following:

I am looking for a way to increase the size of the "slash" (/) that separates the numerator and denominator. I know I could use a normal \frac instead of \nicefrac but I like how it looks when num/den are displayed side by side.

Is there any way I can force the fraction to look more like the first pictured one?

• welcome to tex.se! please, always provide complete small document (beginning with \documentclass followed by necessary preamble and ending with \end{document}). Dec 12 '18 at 16:50
• My apologies, I will do so in future Dec 12 '18 at 17:10

There are many ways. You will find two different in some variation below. The last one looks more like your desired output.

\documentclass{memoir}
\usepackage{amsmath,xfrac,mathtools}

\begin{document}
\begin{align}
\alpha(k)
&=\frac{1}{(N-k)}
\left.
\left(\sum_{i=k+1}^{N} \lambda_i \right)
\right/
\left(\prod_{i=k+1}^N \lambda_i \right)^{\sfrac 1{(N-k)}}\label{eq:alphaK}\\
&=\frac{1}{N-k}
\left.
\left(\sum_{i=k+1}^{N} \lambda_i \right)
\middle/
\left(\prod_{i=k+1}^N \lambda_i \right)^{\frac 1{N-k}}
\right.\\
&=\frac{1}{N-k}
\biggl(\,\sum_{i=k+1}^{N} \lambda_i \biggr)
\bigg/
\biggl(\,\prod_{i=k+1}^N \lambda_i \biggr)^{1/{(N-k)}}\\
%space added as suggested by Enrico Gregorio
&=\frac
{\sum\limits_{i=k+1}^{N} \lambda_i}
{(N-k)\, \sqrt[N-k]{\prod\limits_{i=k+1}^N\lambda_i}}
&\geq 1 \textup{ (by the AM–GM inequality)}
\end{align}
\end{document}


Remarks.

• in your solutions you can omit \displaystyle in both "fraction" terms. and if you use align, please add ampersands before equal signs. Dec 12 '18 at 17:07
• @Zarko Right, I did not noticed that it was there. Dec 12 '18 at 17:10
• +1, for considering my comment :-) Dec 12 '18 at 17:25
• @DavidScott You are welcome. Dec 12 '18 at 23:23

a small variation of CampanIgnis answer (since he was to fast for my frozen fingers :-( ):

\documentclass{article}
\usepackage{nccmath}

\begin{document}
$$%\label{eq:alphaK} \alpha(k) = \frac{1}{(N-k)} \left(\sum_{i=k+1}^{N} \lambda_i \middle) \!\middle/\! \middle(\prod_{i=k+1}^N \lambda_i \right)^{\mfrac{1}{N-k}}$$
\end{document}


• Very nice :-)...for the frozen fingers. Dec 12 '18 at 21:15
• @Zarko I then recommend you some お茶 for your fingers. Dec 12 '18 at 23:13
• @Zarko I have a general question on your solution: If one of the products would be much, much larger then all other three delimiters would grow, too. Is that intentional? Dec 12 '18 at 23:20
• @CampanIgnis, oh, it would be sufficient if I had a warm glove on my afternoon the walk :-). about size of nominator and donominator: size is slašš line depends on taste. in such cases will rather use the following aproach: \left(<nominator>\right)\left(<denominator>\right)^{-1} Dec 12 '18 at 23:34