I'm having a hard time trying to get a properly aligned inequations involving fractions in KaTeX. The best output I have got is with the array environment:
\begin{array}{crccclc}
z\in\Bbb R^+, & 0 &\le& x-z\ffrac{x}{z} &\lt& z & (8)\\[3pt]
& z\ffrac{x}{z} &\le& x &\lt& (z+1)\ffrac{x}{z} &(9)
\end{array}
The problem is the array environment displays formulas in inline style. How could I force arrays to print fractions, sums, etc, in a non-inline style so they take more height?
For those who don't use KaTeX, here's an answer that use the alignat environment of the amsmath environment.
\documentclass{article}
\usepackage{array,amssymb,mathtools}
\DeclarePairedDelimiter{\floor}{\lfloor}{\rfloor}
\newcommand\ffrac[2]{\floor*{\frac{#1}{#2}}}
\newlength\mylen
\settowidth\mylen{$\displaystyle x-z\ffrac{x}{z}$} % measure width of middle part
\begin{document}
\begin{alignat}{4}
z\in\Bbb{R}^+, &\quad& 0 &\le{}&& x-z\ffrac{x}{z} &{}<{}& z \\[1ex]
&& z\ffrac{x}{z} &\le{}&& \parbox{\mylen}{\centering$x$} &{}<{}& (z+1)\ffrac{x}{z}
\end{alignat}
\end{document}
alignat add them automatically in LaTeX? KaTeX have a similar environment called alignedat but it doesn't add them.
amsmath package provides environments called align, alignat, aligned, and alignedat. The former two are standalone environments that provide equation numbering; the latter two are meant to be used inside a larger, encasing environment and do not provide their own numbering mechanism.
A variant of @Mico's solution, using the \DeclarePairedDelimiterX command, from mathtools:
\documentclass{article}
\usepackage{mathtools}
\usepackage{amssymb}
\DeclarePairedDelimiterX{\ffrac}[2]{\lfloor}{\rfloor}{\frac{#1}{#2}}
\begin{document}
\setcounter{equation}{7}
\begin{alignat}{3}
z\in\Bbb R^+, \qquad 0 &\le x- & & z\ffrac*{x}{z} & & < z \\[3pt]
z\ffrac*{x}{z} &\le & & x & & < (z+1)\ffrac[\bigg]{x}{z}
\end{alignat}
\end{document}
I just found out that KaTeX has the darray environment that does exactly what I'm asking for.
I add a small answer (it similar to a comment). I suggest to use this link https://katex.org/docs/support_table.html, a simple guide of KaTeX specific for the table.
\begin{darray}{cc}
a & b \\
c & d
\end{darray}
In the left bar you can find also the guide of KaTeX. I add also a link of MathJaX that it is used in Math.SE:
https://math.meta.stackexchange.com/questions/5020/mathjax-basic-tutorial-and-quick-reference
