Standard math environment for equally-spaced columns of expressions?

Question

I often need a display environment which would let me easily present equally-spaced expressions in the same line, with content on successive lines appearing centred at the same x-coordinate as content on the first line. I can sort of get the effect I want like this:

\begin{align*}
x+y && e^{2 \pi i} && \sigma
\\
\text{First} && \text{Second} && \text{Third}
\end{align*}

But it's not quite perfect, as the 'columns' appear right-aligned, not centred.

Of course I can achieve this easily enough using an array. But then I have to set the spacing between the columns myself, which the align environment does for me automatically. I just wonder if any of the standard math environments can do this already. I would like to be able to code it like this:

\begin{myenvironment*}
x+y & e^{2 \pi i} & \sigma
\\
\text{First} & \text{Second} & \text{Third}
\end{myenvironment*}

Answer 1

For equally-spaced columns (different from equal-width columns), you could put your contents in a fixed-width tabular* environment:

\documentclass{article}
\usepackage{lipsum,array,amsmath}
\begin{document}
​​​​​​​​​​​​​​​​​​​​​​​​\lipsum[1]
\newcolumntype{E}{@{}c@{}}% begin-/end-column definitions
\noindent\begin{tabular*}{\textwidth}{@{\extracolsep{\fill}}E*{3}{>{$}c<{$}}E}
  & x+y & e^{2 \pi i} & \sigma & \\
  & \text{First} & \text{Second} & \text{Third} &
\end{tabular*}
\lipsum[2]
\end{document}
​

I define a new columntype E used merely as a spacer for the first/last columns. Also, the addition of @{\extracolsep{\fill}} adds stretch before/after each column to space things out evenly across \textwidth. Using *{3}{>{$}c<{$}} allows for 3 similarly defined columns (centered c and typeset in math mode $...$).

Of course, this requires you to know how many columns you want to typeset, since you're using the tabular* environment. Although this is not as noticeable, you might want to add \renewcommand{\tabcolsep}{0pt} and scope {...} it around your tabular* environment in order to remove the spacing caused by the E column type. For example the code

\newcolumntype{E}{@{}c@{}}% begin-/end-column definitions

{\renewcommand{\tabcolsep}{0pt}% No \tabcolsep
\noindent\begin{tabular*}{\textwidth}{@{\extracolsep{\fill}}E*{3}{>{$}c<{$}}E}
  & x+y & e^{2 \pi i} & \sigma & \\
  & \text{First} & \text{Second} & \text{Third} &
\end{tabular*}}

\noindent\begin{tabular*}{\textwidth}{@{\extracolsep{\fill}}E*{3}{>{$}c<{$}}E}
  & x+y & e^{2 \pi i} & \sigma & \\
  & \text{First} & \text{Second} & \text{Third} &
\end{tabular*}

produces this marginal difference