Create display version of array environment

Question

I find array environment pretty useful for aligning some blocks of equations, especially more flexible way of aligning each column as a whole, unlike alugn, however it has a couple of issues

1. You have to put array inside another math environment
2. All math like fractions, sum limits, integrals look small, because array isn't a display environment
3. Spacing between rows is different from other amsmath environments like align. I want spacing to be exactly the same as in gather for example

Here's a comparison with align

The solution that I'm looking for has to take care of all listed issues above, but also keep the key feature of array: full control of columns type: l, r and especially c and all other properties like @{}, >{} <{}, vertical lines c|c , etc.

Basically I need a standalone display variant default array that has same spacing as other amsmath environments. Making each row being labeled isn't the most important thing for me, but it would be nice to have such an option.

---

Here's the "MWE" of desired environment and it's output

\documentclass{article}

\begin{document}

\begin{displayArray}{ *{3}{c} }
a^2+b^2=c^2 & \frac{m}{n} = q & 1+2+3+4+5=15 \\
\sum_{i=1}^n & \int_a^bf(x)dx=F(x) & k=j
\end{displayArray}

\end{document}

Answer 1

This is the way align is meant to be used:

\documentclass{article}
\usepackage{amsmath}
\begin{document}
some text
\begin{align}
\frac{a+b}{c} &= d &\quad x+y &=z \\
\frac{k}{i-j} &= n &\quad m &=n
\end{align}
some more text
\end{document}

Answer 2

I use IEEEeqnarray a lot, so much that it's actually the only math environment I use at all. It can do a lot of stuff and is perfectly suitable for your example. I did not have to modify your MWE much to get the output you want to have:

\documentclass{article}

\usepackage{IEEEtrantools}

\begin{document}

\begin{IEEEeqnarray}{C'C'C}
a^2+b^2=c^2 & \frac{m}{n} = q & 1+2+3+4+5=15 \\
\sum_{i=1}^n & \int_a^bf(x)dx=F(x) & k=j
\end{IEEEeqnarray}

\end{document}

So the things I had to do were loading the package, changing the column specification a bit (no repetition operator is possible for IEEEeqnarray) and change the environment name of course. That's it and the output is:

Regarding the column specification: Default spacing between the columns is a bit different than in your example, but this can be easily changed by inserting spacing modifiers between the columns, for instance ' gives 1em of spacing between columns.

More Details

IEEEeqnarray works with column specifications and you place a & between every column, similar to a table. For simple things, align can do the same but I always find align clumsy and difficult to grasp for more complex cases. For example, I had some struggles with putting aligned text at the right of equations. IEEEeqnarray has extra column types for exactly this!

In general, IEEEeqnarray uses less abstraction from the underlying \halign than other environments, which I think is a good thing in this case. You can define your own column types as well as inter-column glue in an easy way and at least for me it's more logical where the ampersands have to go. So this is a clear recommendation to use IEEEeqnarray wherever possible :) For simple equations with aligned equal-signs, my go-to column specification is {rCl}, works like a charm.

Answer 3

You could always define new column types to set all math in display style, and wrap an array into another environment where \arraystretch is larger.

\documentclass{article}
\usepackage{amsmath}
\usepackage{array}
\newcolumntype{C}{>{\displaystyle}c}
\newcolumntype{L}{>{\displaystyle}l}
\newcolumntype{R}{>{\displaystyle}r}
\newenvironment{displayArray}[1]{%
    \let\currentstretch\arraystretch
    \renewcommand*{\arraystretch}{2}
    \[\begin{array}{#1}
}{%
    \end{array}\]
    \let\arraystretch\currentstretch
}
\begin{document}

\begin{displayArray}{LR}
\frac{a+b}{c} = d & x+y=z \\
\frac{k}{i-j} = n & m=n
\end{displayArray}

\end{document}

Answer 4

Here is a possible solution with tabularray package: cells = {mode=dmath} sets display math mode for all cells.

\documentclass{article}
\usepackage{tabularray}
\usepackage{amsmath}
\NewTblrEnviron{displayArray}
\SetTblrInner[displayArray]{
  cells = {mode=dmath},
  colsep = 5pt,
  rowsep = 0.5\jot,
}
\begin{document}

\section{align}

\begin{align}
a^2+b^2=c^2 && \frac{m}{n} = q && 1+2+3+4+5=15 \\
\sum_{i=1}^n && \int_a^bf(x)dx=F(x) && k=j
\end{align}

\section{displayArray}

\begin{displayArray}{ *{3}{c} }
a^2+b^2=c^2 & \frac{m}{n} = q & 1+2+3+4+5=15 \\
\sum_{i=1}^n & \int_a^bf(x)dx=F(x) & k=j
\end{displayArray}

\end{document}