Centering text in a tabular environment

Question

Good day to all,

This look not beautiful for me, I want the text is centred in the box, especially $\frac{1}{s^n}$. Your help is much appreciated.

\documentclass{report}

\usepackage{amsmath} 

\begin{document}
\begin{table}[H]\centering\label{laplaceintegral}
\begin{tabular}{|c|c|c|}
\hline 
Item & $\text{Functions ($t$ domain)}$ & $\text{Laplace Transforms ($s$ domain)}$\\
\hline\hline
1&$\int_0^t x(\tau)d\tau$ & $\displaystyle\frac{1}{s}\cdot X(s)$\\ \hline
2&$\underbrace{\int_0^{t}\ldots\int_0^{t_3}\int_0^{t_2}}_{n\text{times}} %
    x\left(\tau_1\right)d\tau_1dt d\tau_2\ldots d\tau_n$ %
    & $\displaystyle \frac{1}{s^n}\cdot X(s)$ \\ \hline
\end{tabular}
\caption{Laplace transform of integral}
\end{table}

\end{document}

thank you in advance.

Answer 1

I would suggest removing the horizontal rules separating the row entries, as well as all the vertical rules - the tabular alignment already encourages a columnar context naturally. Read more about this in the booktabs documentation.

Following booktabs' suggestion, the spaces things out a little:

\documentclass{report}
\usepackage{float}% http://ctan.org/pkg/float
\usepackage{amsmath}% http://ctan.org/pkg/amsmath
\usepackage{booktabs}% http://ctan.org/pkg/booktabs
\newcommand{\dt}{\mathrm{d}t}
\begin{document}

\begin{table}%[H]
  \centering
  \begin{tabular}{ccc}
    \toprule
    Item & $\text{Functions ($t$~domain)}$ & $\text{Laplace Transforms ($s$~domain)}$ \\
    \midrule
    1 & $\int_0^t x(\tau)d\tau$ & $\displaystyle\frac{1}{s}\cdot X(s)$ \\
    2 & $\underbrace{\int_0^{t}\ldots\int_0^{t_3}\int_0^{t_2}}_{n~\text{times}} 
      x\left(\tau_1\right)d\tau_1\dt d\tau_2\ldots d\tau_n
      \vphantom{\overbrace{\int_0^{t}\ldots\int_0^{t_3}\int_0^{t_2}}^{n~\text{times}}}$ & 
      $\displaystyle \frac{1}{s^n}\cdot X(s)$ \\
    \bottomrule
  \end{tabular}
  \caption{Laplace transform of integral}
\end{table}

\end{document}

I've added a \vphantom in cell (2,2) that adds some vertical space equivalent to the drop initiated by "n times". Using \\[<len>] (where <len> is some length) would also have worked.

Finally, you need to place the \label after \caption, always. See Why does an environment's label have to appear after the caption?