There are other similar questions, all with different answers, but I could not find one which achieves what I want. In the table below, the spacing between the numbers is too wide. How can I shrink it a bit?

```
\newcommand{\testmode}[2] {
\begin{tabular}{c}
\textbf{#1} \\ \textbf{d=#2}
\end{tabular}
}
\begin{table}[ht]
\begin{tabular}{l | c c c | c c c |}
\cline{2-7}
& \multicolumn{3}{c|}{\textbf{Single}} & \multicolumn{3}{c|}{\textbf{Double}} \\
\cline{2-7}
& \testmode{Scalar}{1} & \testmode{SSE-4}{4} & \testmode{AVX-2}{8} & \testmode{Scalar}{1} & \testmode{SSE-4}{2} & \testmode{AVX-2}{4} \\
\hline
\multicolumn{1}{|c|}{\textbf{Eytzinger} } & 209.86 & 370.18 & 411.25 & 180.85 & 245.37 & 262.61 \\
\multicolumn{1}{|c|}{\textbf{Classic Offset} } & 213.28 & 363.35 & 476.10 & 209.04 & 247.02 & 208.63 \\
\hline
\end{tabular}
\caption{Throughput in millions of searches per second with vector $X$ of size 15}
\label{tab:results0}
\end{table}
```

## Best Answer

In your example you have doubled the column separation using a

`tabular`

inside a`tabular`

. Note: LaTeX adds a distance of`\tabcolsep`

before and after each column. In your case you have such a distance before and after the column of the inner tabular of`\testmode`

and before and after the column of the outer tabular. To avoid this, you should add`@{}`

before the first column of the inner tabular and after the last column of the inner tabular:To explain some more: By default LaTeX adds

`\hskip\tabcolsep`

before it starts a column and after it has finished a column. So you have the distance`\tabcolsep`

before the first and after the last column and`2\tabcolsep`

between two columns. If you use`@{…}`

the code of the argument of`@`

is addedinstead of the distance. So`@{}`

just removes the distance.Additional note: I would recommend to avoid vertical rules in tables (see the manual of package

`booktabs`

) and to use package`siunitx`

for number columns. And I would not center the elements of the first table row but left-align them. And because`d=…`

in the table head is something like math, you should set it in math mode. In this case I also would not make it bold (using, e.g.,`\boldmath`

), because font attributes in math have mostly a semantic (e.g, bold is often used for vectors or sets).