\begin{table}%t1
      \caption{CPU timing information for assembling the BEM matrices, for solving the linear systems of equations with the Gauss solver, the LU solver, or the GMRES(50) solver with various settings of $\varepsilon$, and for extrapolating the fields for 15 layers (CPU time in seconds).}
      \label{t:timing}
      %\centering
\par
      \begin{tabular}{lllllllllll}
      \hline
      \hline
Degrees of freedom $(N)$ &1023 & 1443 & 1935 & 2499 & 3135 & 3843 & 4623 & 5475 & 6399  & 7395\\
\hline
Gauss                 &12.53   &34.64  &163.67 &850.44 &2524.63 &5938.27 &12~783.19 &21~886.44  &38~032.91 &61~239.19\\
LU                    &0.86    &3.66   &10.34  &23.22  &46.44   &85.94   &149.66   &248.36    &395.78   &611.64\\
GMRES($50,10^{-16}$)  &2.97    &6.39   &12.48  &22.95  &37.41   &59.41   &88.83    &137.97    &191.08   &271.03\\
GMRES($50,10^{-6}$)   &0.89    &1.86   &3.50   &6.06   &10.08   &16.06   &24.41    &35.44     &49.54    &69.69\\
GMRES($50,10^{-2}$)   &0.19    &0.41   &0.73   &1.23   &1.84    &2.80    &4.03     &5.66      &7.70     &10.75\\
\hline
Assembling            &0.88   &1.78  &3.27  &5.50    &9.33   &15.48   &22.88    &32.39     &44.55    &59.14\\
Extrapolation         &15.72   &31.59  &56.81  &95.47  &151.05  &227.31  &330.59   &478.05    &644.13   &863.23\\
\hline
\end{tabular}
   \end{table}