vertical spacing in nested fraction

Question

I have complicated math expression:

Vertical spacing between text and fraction line is too small.
I tried to define new \frac command (with amsmath package) with adjustable vertical spaces. As you can see, the result is not satisfying:

\documentclass[a4paper,fleqn,leqno]{article}
\usepackage{polyglossia}
\usepackage{color,pifont,fontspec}
\usepackage[top=2.54cm,bottom=2.54cm,left=2.54cm,right=2.54cm]{geometry}
\usepackage{tikz,tikz-3dplot,graphicx}
\usepackage{mathtools,breqn,amsmath}
\usepackage[fontsize=12]{scrextend}
\usepackage{array,multirow}
\usepackage{pgfplots}
\DeclareMathSizes{12}{14}{14}{10}
\newcommand{\myfrac}[3][0pt]{\genfrac{}{}{}{}{\raisebox{#1}{$#2$}}{\raisebox{-#1}{$#3$}}}
\begin{document}
\begin{dmath*}[breakdepth={0},style={\mathindent=0pt},spread={10pt}]
{n=\myfrac[3pt]{\myfrac[3pt]{0,0625N+0,0215}{2}-0,043}{\myfrac[3pt]{\myfrac[3pt]{\scriptstyle 0,0625N+0,0215}{\scriptstyle 2}-0,043}{\myfrac[3pt]{\scriptstyle N}{\scriptstyle 2}-1}+0,0215}}
\end{dmath*}
\end{document}

How can I enlarge verticall spacing in whole fraction?

Answer 1

In such cases I'd add a \mathstrut which however is not sufficient if the fraction is part of a denominator. For this situation, \big| seems to do.

\documentclass{article}
\usepackage{amsmath,xparse}

\NewDocumentCommand{\qfrac}{smm}{%
  \dfrac{\IfBooleanT{#1}{\vphantom{\big|}}#2}{\mathstrut #3}%
}

\begin{document}

Without adjustment
\[
n=\frac
   {\qfrac{0{,}0625N+0{,}0215}{2}-0{,}043}
   {\qfrac
     {\qfrac{0{,}0625N+0{,}0215}{2}-0{,}043}
     {\qfrac{N}{2}-1+0{,}0215}
   }
\]

With adjustment
\[
n=\frac
   {\qfrac{0{,}0625N+0{,}0215}{2}-0{,}043}
   {\qfrac
     {\qfrac*{0{,}0625N+0{,}0215}{2}-0{,}043}
     {\qfrac*{N}{2}-1+0{,}0215}
   }
\]

\end{document}

The \qfrac* version is to be used when the fraction is in a denominator.

Note {,} so there's no space after the comma.

The picture seems to hint that the top minus sign next to 0,043 is not aligned with the fraction line, but it's just due to pixel rounding. Here's the detail at maximum magnification.

Answer 2

Vertical spacing adjustments are unnecessary if you use the \cfrac machinery ("continued fractions") to typeset the complicated nested fraction expression.

\documentclass[a4paper,fleqn,leqno]{article}
\usepackage{polyglossia}
\usepackage{fontspec}
\usepackage[margin=2.54cm]{geometry}
\usepackage{amsmath}
\usepackage[fontsize=12]{scrextend}
\begin{document}
\[
n=\cfrac{\cfrac{0{,}0625N+0{,}0215}{2}-0{,}043}
        {\cfrac{\cfrac{0{,}0625N+0{,}0215}{2}-0{,}043}
               {\cfrac{N}{2}-1}
        +0{,}0215}
\]
\end{document}