I would like to add an equation in a multirow cell, using tabular and a defined width. It worked everywhere in the table, except for a cell which is a multirow of two other multirows. In this case, I get an error. (The cell is indicated as HERE in the attached picture). Do you have any idea how to solve it? Thank you!

\RequirePackage[patch]{kvoptions}
\documentclass{DissOnlineLatex}
\usepackage{amsmath}
\usepackage{mathtools, eqparbox}
\usepackage[makeroom]{cancel}
\newcommand{\eqbox}[2][]{\eqmakebox[#1][l]{\mbox{#2~}}}
\usepackage{dsfont}
\usepackage{longtable}
\usepackage{supertabular}
\usepackage{tabu}
\usepackage{multirow, tabularx}
\usepackage{multicol}
\newcolumntype{T}{>{\centering\arraybackslash\hsize=0.4\hsize}X}
\newcolumntype{V}{>{\centering\arraybackslash\hsize=0.65\hsize}X}
\newcolumntype{s}{>{\hsize=0.2\hsize}X}
\newcolumntype{b}{>{\hsize=1.0\hsize}X}
\newcolumntype{d}{>{\hsize=0.5\hsize}X}
\usepackage{tabulary}
\usepackage{longtable}
\usepackage{array}
\newcolumntype{P}[1]{>{\centering\arraybackslash}p{#1}}
\newcolumntype{M}[1]{>{\centering\arraybackslash}m{#1}}
\newcolumntype{L}[1]{>{\raggedleft\arraybackslash}p{#1}}
\usepackage{lscape}
\usepackage{xcolor}
\usepackage{graphicx}
\usepackage{caption}
\usepackage{subcaption}
\usepackage[outdir=./]{epstopdf}
\usepackage{multirow}
\usepackage{booktabs}
\usepackage{float}
\usepackage{rotating}
\usepackage{SIunits}
\usepackage{blindtext}
\usepackage[latin1]{inputenc}
\usepackage[
backend=biber,
style=numeric,
sortcites,
sorting = anyvt,
isbn=false,
url=false,
doi=false,
eprint=false,
backref,
natbib,
hyperref
]{biblatex}
\begin{document}

\begin{table}[htb]
\renewcommand\tabularxcolumn[1]{m{#1}}
\caption{Necessary liquid-gas ratios for concave and convex equilibrium lines.}
\label{table:Nec_LG}
\setlength\abovedisplayskip{0pt}
\setlength\belowdisplayskip{0pt}
\centering
\begin{tabular}{|c|M{4.0cm}|M{2.0cm}|M{3.0cm}|M{4.0cm}|}
\hline
\textbf{LG} & \textbf{Description} &\textbf{Goal} & {\textbf{Case}} & {\textbf{LG=}}\\
\hline
\hline
\multirow{2}[4]{*}{$LG_a$} & \multirow{2}[4]{=}{Minimal LG for maximal (de)humidification} & \multirow{2}[4]{*}{$\omega_t=\omega_t^*$} & Convex & $$\frac{\partial \omega^*}{\partial \xi}\Bigr\rvert_{\xi = \xi_t} \label{eq:ratio_a_pinch_convex}$$ \\
\cline{4-5}          &       &       & Concave & \multirow{2}{*}{
HERE
} \\
\cline{1-4}    \multirow{2}[4]{*}{$LG_d$} & \multirow{2}[4]{=}{Maximal LG for maximal dilution or regeneration} & \multirow{2}[4]{*}{$\xi_b=\xi_b^*$} & Concave &  \\
\cline{4-5}          &       &       & Convex & $$\frac{\partial \omega^*}{\partial \xi}\Bigr\rvert_{\xi = \xi_b^*} \label{eq:ratio_d_pinch_convex}$$ \\
\hline
\hline
\multirow{4}{*}{$LG_h$} & \multirow{4}{=}{Minimal LG for specified (de)-humidification} & \multirow{4}{*}{$\omega_t=\omega_{t,goal}$}& Straight, concave and convex $LG_h\le LG_d$& $$\frac{\omega_b-\omega_{t,goal}}{\xi_b^*-\xi_t} \label{eq:ratio_h_pinch_concave}$$\\
\cline{4-5}
&  &  & convex $LG_h\ge LG_d$ & $$\frac{\omega^*(\hat{\xi})-\omega_{t,goal}}{\hat{\xi}-\xi_t} \label{eq:ratio_h_pinch_convex}$$ \\
\hline
\multirow{4}{*}{$LG_r$} & \multirow{4}{=}{Maximal LG for specified  dilution or regeneration} & \multirow{4}{*}{$\xi_b=\xi_{b,goal}$}& Straight, concave and convex $LG_r\ge LG_a$& $$\frac{\omega_b-\omega_t^*}{\xi_{b,goal}-\xi_t} \label{eq:ratio_r_pinch_concave}$$\\
\cline{4-5}
&  &  & convex $LG_r<LG_a$ & $$\frac{\omega_{b}-\omega^*(\hat{\xi})}{\xi_{b,goal}-\hat{\xi}} \label{eq:ratio_r_pinch_convex}$$ \\
\hline
\hline
\end{tabular}
\end{table}

\end{document}
• Umm, is the DissOnlineLatex document class available online somewhere?
– Mico
Sep 9 '20 at 19:22
• Incidentally, what's the purpose of running \renewcommand\tabularxcolumn[1]{m{#1}} if you're not going to use a tabularx column?
– Mico
Sep 9 '20 at 19:25
• Thanks Miko for trying. I forgot to upload DissOnlineLatex. But the file works with article anyway. I just used this \renewcommand\tabularxcolumn[1]{m{#1}} for other tables I have in may document. Next time I'll try to prepare the code better. A possible solution has already been posted by Andrew. Have a nice day!
– CRH
Sep 10 '20 at 10:10

I don't have the DissOnlineLatex document class so I have used article in what follows.

I would not put equation environments inside a tabular environment and I would have thought that this would lead to a pile of errors. So, I am surprised that you only get one error inside the \multirow cells. I guess that this works because you are using an M-column type. If you want to put an equation environment inside the \multirow cell then the obvious thing to do is to put the equation inside a minipage environment. Using this seems to do what you want:

Setting the width of the minipage environment to \linbewidth should, in theory, give the correct width. I found by trial and error that using 0.97\linewidth worked better in that this made the equation number in this cell align properly with the other equation numbers. Here is your modified MWE:

\RequirePackage[patch]{kvoptions}
\documentclass{article}
\usepackage{amsmath}
\usepackage{mathtools, eqparbox}
\usepackage[makeroom]{cancel}
\newcommand{\eqbox}[2][]{\eqmakebox[#1][l]{\mbox{#2~}}}
\usepackage{dsfont}
\usepackage{longtable}
\usepackage{supertabular}
\usepackage{tabu}
\usepackage{multirow, tabularx}
\usepackage{multicol}
\newcolumntype{T}{>{\centering\arraybackslash\hsize=0.4\hsize}X}
\newcolumntype{V}{>{\centering\arraybackslash\hsize=0.65\hsize}X}
\newcolumntype{s}{>{\hsize=0.2\hsize}X}
\newcolumntype{b}{>{\hsize=1.0\hsize}X}
\newcolumntype{d}{>{\hsize=0.5\hsize}X}
\usepackage{tabulary}
\usepackage{longtable}
\usepackage{array}
\newcolumntype{P}[1]{>{\centering\arraybackslash}p{#1}}
\newcolumntype{M}[1]{>{\centering\arraybackslash}m{#1}}
\newcolumntype{L}[1]{>{\raggedleft\arraybackslash}p{#1}}
\usepackage{lscape}
\usepackage{xcolor}
\usepackage{graphicx}
\usepackage{caption}
\usepackage{subcaption}
\usepackage[outdir=./]{epstopdf}
\usepackage{multirow}
\usepackage{booktabs}
\usepackage{float}
\usepackage{rotating}
\usepackage{SIunits}
\usepackage{blindtext}
\usepackage[latin1]{inputenc}
\usepackage[
backend=biber,
style=numeric,
sortcites,
sorting = anyvt,
isbn=false,
url=false,
doi=false,
eprint=false,
backref,
natbib,
hyperref
]{biblatex}
\begin{document}

\begin{table}[htb]
\renewcommand\tabularxcolumn[1]{m{#1}}
\caption{Necessary liquid-gas ratios for concave and convex equilibrium lines.}
\label{table:Nec_LG}
\setlength\abovedisplayskip{0pt}
\setlength\belowdisplayskip{0pt}
\centering
\begin{tabular}{|c|M{4.0cm}|M{2.0cm}|M{3.0cm}|M{4.0cm}|}
\hline
\textbf{LG} & \textbf{Description} &\textbf{Goal} & {\textbf{Case}} & {\textbf{LG=}}\\
\hline
\hline
\multirow{2}[4]{*}{$LG_a$} & \multirow{2}[4]{=}{Minimal LG for maximal (de)humidification} & \multirow{2}[4]{*}{$\omega_t=\omega_t^*$} & Convex & $$\frac{\partial \omega^*}{\partial \xi}\Bigr\rvert_{\xi = \xi_t} \label{eq:ratio_a_pinch_convex}$$ \\
\cline{4-5}          &       &       & Concave & \multirow{2}{*}{
\begin{minipage}{0.97\linewidth}
$$\label{E:} \frac{\partial \omega^*}{\partial \xi}\Bigr\rvert_{\xi = \xi_b^*}$$
\end{minipage}
} \\
\cline{1-4}    \multirow{2}[4]{*}{$LG_d$} & \multirow{2}[4]{=}{Maximal LG for maximal dilution or regeneration} & \multirow{2}[4]{*}{$\xi_b=\xi_b^*$} & Concave &  \\
\cline{4-5}          &       &       & Convex & $$\frac{\partial \omega^*}{\partial \xi}\Bigr\rvert_{\xi = \xi_b^*} \label{eq:ratio_d_pinch_convex}$$ \\
\hline
\hline
\multirow{4}{*}{$LG_h$} & \multirow{4}{=}{Minimal LG for specified (de)-humidification} & \multirow{4}{*}{$\omega_t=\omega_{t,goal}$}& Straight, concave and convex $LG_h\le LG_d$& $$\frac{\omega_b-\omega_{t,goal}}{\xi_b^*-\xi_t} \label{eq:ratio_h_pinch_concave}$$\\
\cline{4-5}
&  &  & convex $LG_h\ge LG_d$ & $$\frac{\omega^*(\hat{\xi})-\omega_{t,goal}}{\hat{\xi}-\xi_t} \label{eq:ratio_h_pinch_convex}$$ \\
\hline
\multirow{4}{*}{$LG_r$} & \multirow{4}{=}{Maximal LG for specified  dilution or regeneration} & \multirow{4}{*}{$\xi_b=\xi_{b,goal}$}& Straight, concave and convex $LG_r\ge LG_a$& $$\frac{\omega_b-\omega_t^*}{\xi_{b,goal}-\xi_t} \label{eq:ratio_r_pinch_concave}$$\\
\cline{4-5}
&  &  & convex $LG_r<LG_a$ & $$\frac{\omega_{b}-\omega^*(\hat{\xi})}{\xi_{b,goal}-\hat{\xi}} \label{eq:ratio_r_pinch_convex}$$ \\
\hline
\hline
\end{tabular}
\end{table}

\end{document}
• Wow Andrew, this is great. Thanks a lot for your help! I didn't know that it is recommended not to use equations insede tabular (although I managed it after trying a lot of different things). So your way is much simpler and works perfectly. Thanks again :)
– CRH
Sep 10 '20 at 10:06