# 'Undefined control sequence' error when typesetting table

The error is

Undefined control sequence.

Here is the code:

\begin{table}[htb!!]
\center
\begin{tabular}{|c|c|c|c|c|c|}
\hline
\multicolumn{2}{|c|}{Experiment} & Initial tip deflection & frequency $\omega$ & base acceleration $a_b$ & Magnet gap $\delta$ \\
\hline
TC 1 &
\begin{tabular}{c}a \\ b\end{tabular} & \begin{tabular}{c} $10^{-3}\ mm$ \\ $5\ mm$\end{tabular} & Uniform $\in [9,14]\ Hz$ & $1\ m/s^2$ & $50\ mm$ \\
\hline
TC 2 &
\begin{tabular}{c}a \\ b\end{tabular} & \begin{tabular}{c} $10^{-3}\ mm$ \\ $5\ mm$\end{tabular} & $11.5 \ Hz$ & Uniform $\in \left[ 0.5,1.5 \right]\ m\s^2$ & $50\ mm$\\
\hline
TC 3 &
\begin{tabular}{c}a \\ b\end{tabular} & \begin{tabular}{c} $10^{-3}\ mm$ \\ $5\ mm$\end{tabular} & $11.5\ Hz$ & $1\ m/s^2$ & Uniform $\in [45,55]\ mm$\\
\hline
\multicolumn{2}{|c|}{TC 4} & Uniform $\in [0,5]\ mm$ & Uniform $\in [9,14]\ Hz$ & Uniform $\in [0.5,1.5]\ m/s^2$ & Uniform $\in [45,55]\ mm$ \\
\hline
\end{tabular}
\caption{Uncertain parameters/initial conditions }\label{table_exp}
\end{table}

• Welcome to TeX.SX! Please make your code compilable (if possible), or at least complete it with \documentclass{...}, the required \usepackage's, \begin{document}, and \end{document}. That may seem tedious to you, but think of the extra work it represents for TeX.SX users willing to give you a hand. Help them help you: remove that one hurdle between you and a solution to your problem. – adn Apr 15 '15 at 17:42
• Use \centering instead of \center (which is used by \begin{center}). – John Kormylo Apr 15 '15 at 17:44
• Remember to accept the answer you find most useful (if, indeed, any of them are useful to you). – Svend Tveskæg Apr 27 '15 at 2:48

! Undefined control sequence.
l.13 ... Uniform $\in \left[ 0.5,1.5 \right]\ m\s  You have \s instead of /s Since David has already answered your question, I'll allow myself to 'just' improve on the aesthetics of the table: \documentclass{article} \usepackage[margin = 3.5cm]{geometry} % avoid overfull \hbox' warning \usepackage[tableposition = top]{caption} % captions \usepackage{booktabs} % horizontal lines in tables \usepackage[per-mode = symbol]{siunitx} % physical quantities and SI units % shortcut \newcommand*\mr[2]{\begin{tabular}{c}#1\\#2\end{tabular}} \begin{document} \noindent \textsf{Note:} Let$U[a,b]$denote the uniform on the closed interval from$a$to$b$. \begin{table}[htbp] \centering \caption{Uncertain parameters/initial conditions.} \label{table_exp} \begin{tabular}{*{6}{c}} \toprule \multicolumn{2}{c}{Experiment} & Initial tip deflection & Frequency,$\omega$& Base acceleration,$a_{\textnormal{b}}$& Magnet gap,$\delta$\\[0.5ex] & & \si{\mm} & \si{\Hz} & \si{\m\per\square\s} & \si{\mm} \\ \midrule TC 1 & \mr{a}{b} & \mr{$10^{-3}$}{$5$} &$U[9,14]$&$1$&$50$\\ \midrule TC 2 & \mr{a}{b} & \mr{$10^{-3}$}{$5$} &$11.5$&$U[0.5, 1.5]$&$50$\\ \midrule TC 3 & \mr{a}{b} & \mr{$10^{-3}$}{$5$} &$11.5$&$1$&$U[45, 55]$\\ \midrule TC 4 & &$U[0,5]$&$U[9,14]$&$U[0.5, 1.5]$&$U[45, 55]$\\ \bottomrule \end{tabular} \end{table} \end{document}  A few suggestions: • Don't use vertical lines in table; they disturb the more than they help. • Use the siunitx package to typeset the numbers and physical units in the table. • Use the booktabs package to get a better thickness of -- and spacing around -- the horizontal rules. • Use the caption package with the option tableposition = top to get better spacing between the caption and the table. • Use the syntax *{<number of columns>}{<column type>} where possible to shorten the code. • Structure the input code to make it look like the output to get a better overview of it. Here is the corrected code. Notice that the lines giving error need to be adjusted to eliminate m\s^2 and include the corrected m/s^2 for units. \begin{table}[htb!!] \centering \begin{tabular}{|c|c|c|c|c|c|} \hline \multicolumn{2}{|c|}{Experiment} & Initial tip deflection & frequency$\omega$& base acceleration$a_b$& Magnet gap$\delta$\\ \hline TC 1 & \begin{tabular}{c}a \\ b\end{tabular} & \begin{tabular}{c}$10^{-3}\ mm$\\$5\ mm$\end{tabular} & Uniform$\in [9,14]\ Hz$&$1\ m/s^2$&$50\ mm$\\ \hline TC 2 & \begin{tabular}{c}a \\ b\end{tabular} & \begin{tabular}{c}$10^{-3}\ mm$\\$5\ mm$\end{tabular} &$11.5 \ Hz$& Uniform$ \in \left[ 0.5,1.5 \right]\ m/s^2 $&$50\ mm$\\ \hline TC 3 & \begin{tabular}{c}a \\ b\end{tabular} & \begin{tabular}{c}$10^{-3}\ mm$\\$5\ mm$\end{tabular} &$11.5\ Hz$&$1\ m/s^2$& Uniform$\in [45,55]\ mm$\\ \hline \multicolumn{2}{|c|}{TC 4} & Uniform$\in [0,5]\ mm$& Uniform$\in [9,14]\ Hz$& Uniform$\in [0.5,1.5]\ m/s^2$& Uniform$\in [45,55]\ mm\$ \\
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