How to add more space underneath and above a horizontal line in tabu?

Question

I'm having the following table in my document:

\documentclass[12pt]{article}
\usepackage{tabu}
\begin{document}
\[
    \begin{tabu} {c | c c c c c c}
    \firsthline
        f & a_{11} & a_{12} & a_{21} & a_{22} & b_1 & b_2 \\ \hline
        1 & a_{11}^1 & a_{12}^1 & a_{21}^1 & a_{22}^1 & b_1^1 & b_2^1 \\
        \vdots & \vdots & \vdots & \vdots & \vdots & \vdots & \vdots \\
        n & a_{11}^n & a_{12}^n & a_{21}^n & a_{22}^n & b_1^n & b_2^n \\
        \lasthline
    \end{tabu}
\]
\end{document}

The second and the last row are a little bit too close to the horizontal lines. How can I add some more space between them?

---

Update: I tried using \tabulinesep=5pt in the preamble and that looks better.

However, the vdots seem to be placed too much to the bottom now and the lasthline isn't displayed 'bold' anymore. How can I fix this?

Answer 1

I'd probably use array for this but in any case the same \extrarowheight parameter can be used:

\documentclass[12pt]{article}
\usepackage{tabu}
\begin{document}
a
\[
    \begin{tabu} {c | c c c c c c}
    \firsthline
        f & a_{11} & a_{12} & a_{21} & a_{22} & b_1 & b_2 \\ \hline
        1 & a_{11}^1 & a_{12}^1 & a_{21}^1 & a_{22}^1 & b_1^1 & b_2^1 \\
        \vdots & \vdots & \vdots & \vdots & \vdots & \vdots & \vdots \\
        n & a_{11}^n & a_{12}^n & a_{21}^n & a_{22}^n & b_1^n & b_2^n \\
        \lasthline
    \end{tabu}
\]
b
\[\setlength\extrarowheight{2pt}
    \begin{tabu} {c | c c c c c c}
    \firsthline
        f & a_{11} & a_{12} & a_{21} & a_{22} & b_1 & b_2 \\ \hline
        1 & a_{11}^1 & a_{12}^1 & a_{21}^1 & a_{22}^1 & b_1^1 & b_2^1 \\
        \vdots & \vdots & \vdots & \vdots & \vdots & \vdots & \vdots \\
        n & a_{11}^n & a_{12}^n & a_{21}^n & a_{22}^n & b_1^n & b_2^n \\
        \lasthline
    \end{tabu}
\]
\end{document}

Answer 2

tabu's way of doing this is to use \tabulinesep. From manual:

Applying to your code (with some huge space for demo)

\documentclass[12pt]{article}
\usepackage{tabu}
\begin{document}
\[\tabulinesep=1cm    %<--------------------------adjust 1cm
    \begin{tabu} {c | c c c c c c}
    \firsthline
        f & a_{11} & a_{12} & a_{21} & a_{22} & b₁ & b₂ \\ \hline
        1 & a_{11}¹ & a_{12}¹ & a_{21}¹ & a_{22}¹ & b₁¹ & b₂¹ \\
         ⋮  &  ⋮  &  ⋮  &  ⋮  &  ⋮  &  ⋮  &  ⋮  \\
        n & a_{11}^n & a_{12}^n & a_{21}^n & a_{22}^n & b₁^n & b₂^n \\
        \lasthline
    \end{tabu}
\]
\end{document}