Removing vertical space in tables when using minipage/math environments

Question

I'm trying to include equations in a table, I know I need to use minipage to do so. But for some reason it is creating a gap between where the row would usually start and where it does when I include the minipage/math combination.

I have tried using abovedisplayskip to no avail. As well as trimbox and raisebox, both of which succeeded in shifting the equations higher but the text in the first two columns was still offset.

I have the same issue occur with subequations, but the gap is even larger.

Does anyone know why this is happening and/or how to fix it?

\documentclass{article}

\usepackage{xcolor, colortbl}
\usepackage{array,booktabs,tabularx,rotating,amsmath}

\begin{document}
    \begin{sidewaystable}          
        \begin{tabularx}{\textwidth}{X>{$}>{\raggedright\arraybackslash}p{3cm}<{$}l}
        \toprule
        \textbf{Section}  & \textbf{Variables}  & \multicolumn{1}{c}{\textbf{Constraints}}  \\
        \midrule        
        Section 1  & (0 \le a \le 100)\newline
                     (0 \le b \le 100)  &   \begin{minipage}{13cm}
                                                \begin{gather} 
                                                    a+b \ge 42 \\
                                                    a \ge 11
                                                \end{gather}
                                          \end{minipage}\\
        \rowcolor{gray!50}
        Section 2 & (0 \le c \le 100) \newline
                    (0 \le d \le 100) &\begin{minipage}{13cm}
                                            \begin{subequations}                                                    
                                                \begin{gather} 
                                                    \text{Given a bunch of stuff define:} \notag \\                                                        
                                                    \sum_{\mathclap{\substack{a bunch of really\\long stuff}}} (a*d)\\
                                                    c=d                                                          
                                                \end{gather}                                                
                                        \end{subequations}
                                    \end{minipage}\\
             Usually & there & is no vertical space\\
            \bottomrule
        \end{tabularx}     
    \end{sidewaystable}
\end{document}

This is how I would like the table to be aligned. (This was done by putting the the minipage on a separate row and then using raisebox to lift it into place. But this feels very hacky, there must be an actual way to specify the alignment.)

Answer 1

@barbarabeeton @JohnKormylo Thank-you for the assistance to answering this question.

The answer to this post explained why the minipage/math environment combination caused a gap (the etoolbox \kern part). Specifying the minipage placement [t] the corrected the alignment of the first two columns. an additional .4/normalbaselineskip was also added to the \kern adjustment to remove the remaining space above the equation.

\documentclass{article}

\usepackage{xcolor, colortbl}
\usepackage{array,booktabs,tabularx,rotating,amsmath}
\usepackage{adjustbox}
\usepackage{amsthm}
\usepackage{mathtools}

\usepackage{etoolbox}
\makeatletter
\pretocmd\start@gather{%
    \if@minipage\kern-\topskip\kern-\abovedisplayskip\kern-.4\normalbaselineskip\fi
}{}{}
\makeatother

\begin{document}
    \begin{sidewaystable}          
        \begin{tabularx}{\textwidth}{X>{$}>{\raggedright\arraybackslash}p{3cm}<{$}l}
            \toprule
            \textbf{Section}  & \textbf{Variables}  & \multicolumn{1}{c}{\textbf{Constraints}}  \\
            \midrule        
            Section 1  & (0 \le a \le 100)\newline
                         (0 \le b \le 100)  &   \begin{minipage}[t]{13cm}
                                                    \begin{gather} 
                                                        a+b \ge 42 \\
                                                        a \ge 11
                                                    \end{gather}
                                              \end{minipage}\\
            \rowcolor{gray!50}
            Section 2 & (0 \le c \le 100) \newline
                        (0 \le d \le 100) & \begin{minipage}[t]{13cm}
                                                \begin{subequations}   \label{broke}                                                 
                                                    \begin{gather} 
                                                        \text{Given a bunch of stuff define:} \notag \\                                                        
                                                        \sum_{\mathclap{\substack{a bunch of really\\long stuff}}} (a*d)\\
                                                        c=d                                                          
                                                    \end{gather}                                                
                                            \end{subequations}
                                        \end{minipage}\\            
            Usually & there \newline is \newline no & space\\
                \bottomrule
            \end{tabularx}     
        \end{sidewaystable}
\end{document}