Math & Science ⇒ amsmath with multiple alignments on one line, centered

[x42bn6]

Hi all,

Let's just say I want to typeset, ASCII-art style:

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0 <  a  <  b  < 1
1 < a+1 < b+1 < 2

Where the alignments are on the < characters and the contents a, b, a+1 and b+1 are centred in their "cells", but 0, 1, 1 and 2 are right- or left-aligned as if they were the standard align environment.

For example, if I were to put this into a matrix or array environment:

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\begin{array}{rcccccl}
0 & < & a   & < & b   & < & 1 \\
1 & < & a+1 & < & b+1 & < & 2
\end{array}

Of course, this doesn't preserve the intra-line spacing as it's a matrix not an environment like align or alignat. But I think it gets across what I'm trying to do.

Is it possible?

[frabjous]

I'm not entirely sure what you're trying to do. Is the problem with yours just too much space between the "cells"? What about something along these lines?

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\begin{array}{r@{\:<\:}c@{\:<\:}c@{\:<\:}l}
0 & a   &  b   & 1 \\
1 & a+1 &  b+1 & 2
\end{array}

[x42bn6]

Yes, but not with an array (because the between-line spacing is different for an array and, say, align - stick a \dfrac both lines in the same cell and they're too close).

[frabjous]

You can increase the vertical space between the lines in the array by specifying the length after the line break \\:

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\begin{array}{r@{\:<\:}c@{\:<\:}c@{\:<\:}l}
0 & a   &  b   & \dfrac{1}{2} \\[3ex]
1 & a+1 &  b+1 & \dfrac{3}{2}
\end{array}

Alternatively you could load the array package and set the length extrarowheight:

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\documentclass{article}
\usepackage{amsmath,array}
\begin{document}
\setlength{\extrarowheight}{2ex}
\[
\begin{array}{r@{\:<\:}c@{\:<\:}c@{\:<\:}l}
0 & a   &  b   & \dfrac{1}{2} \\
1 & a+1 &  b+1 & \dfrac{3}{2}
\end{array}
\]
\end{document}

[x42bn6]

Do I really have to hack around it?

And is that the space which corresponds to the space in the environments in amsmath?

[frabjous]

Did you see my second suggestion?

I don't know if there are other options, and I don't know what the space is in align environments in AMSMath. Someone else may have some further ideas, but I really don't see this as a hack.