Aligning space characters with non-space characters with alignat

Question

I have the code

\documentclass[12pt]{article}
\usepackage[utf8]{inputenc}
\usepackage{amsmath, amssymb, amsthm}

\begin{document}
\begin{alignat*}{3}
    2^0 &= 1 \pmod{21}, &\qquad 2^4 &\qquad &= 16 \pmod{21},\\
    2^1 &= 2 \pmod{21}, &\qquad 2^5 &= 32   &= 11 \pmod{21},\\
    2^2 &= 4 \pmod{21}, &\qquad 2^6 &= 64   &= 1  \pmod{21}.\\
    2^3 &= 8 \pmod{21}, &\qquad     &\qquad &\qquad
\end{alignat*}
\end{document}

but it's producing this:

How do I get those equals on the right to be lined up?

Welcome to TeX.SX! I get an error when compiling your document, not even producing the output. You have too many &s for your 2 alignment points. — TeXnician, May 03 '18 at 05:29
Thank you! So that number after the alignat command should be a 4? I'll test that out. — Pro Q, May 03 '18 at 05:34
No, it should be 3: count your & characters add 1 and divide that by 2 (rounding up). — TeXnician, May 03 '18 at 05:35
@TeXnician Okay, so it looks like changing it to a 4 got rid of the errors, but still didn't fix the alignment. I'll edit the question. — Pro Q, May 03 '18 at 05:35
Correct, but at least it's compilable now. Are you only interested in an alignat solution? — TeXnician, May 03 '18 at 05:36
@TeXnician Okay, even 3 still has weird alignment. I'll put 3 in the edit. — Pro Q, May 03 '18 at 05:36

score 4 · Accepted Answer · edited May 03 '18 at 09:43

4

An alignat solution, even if I would use an ordinary tabular or array, see here.

\documentclass[12pt]{article}
\usepackage[utf8]{inputenc}
\usepackage{amsmath, amssymb, amsthm}

\begin{document}

\begin{alignat*}{4}
2^0 &= 1 \pmod{21},&\qquad  2^4 & &  & = {} &  16    &  \pmod{21},\\
2^1 &= 2 \pmod{21}, &  2^5 &= 32 & & =   & 11  &   \pmod{21},\\
 2^2 &= 4 \pmod{21}, &  2^6 &= 64 & & =  & 1  &  \pmod{21}.\\
2^3 &= 8 \pmod{21},
\end{alignat*}

\end{document}

edited May 03 '18 at 09:43

Bernard

271,350

answered May 03 '18 at 05:48

CarLaTeX

62,716

Thank you! What do the double &&s do? – Pro Q May 03 '18 at 06:38
@ProQ They change the left/right alignment, see the link in my answer. – CarLaTeX May 03 '18 at 06:47
Shouldn't there be an odd number of ampersands in each row (twice the number of columns – 1)? – Bernard May 03 '18 at 08:19
@Bernard Please correct it! I did it on a hurry and now I can't, thank you! – CarLaTeX May 03 '18 at 08:22
@CarlaTeX: È fatto! – Bernard May 03 '18 at 09:47
@Bernard Grazie! – CarLaTeX May 03 '18 at 10:14

score 2 · Answer 2 · answered May 03 '18 at 10:53

Here, I use a \tabularCenterstack, which has column-alignment features similar to tabular, while providing math spacing features across tabs, similar to align.

\documentclass[12pt]{article}
\usepackage[utf8]{inputenc}
\usepackage{amsmath, amssymb, amsthm, tabstackengine}
\TABstackMath
\begin{document}
\TABbinary
\setstackgap{L}{1.2\baselineskip}
\setstacktabulargap{0pt}
\[\tabularCenterstack{rlrlcrl}{
    2^0 &= 1 \pmod{21}, &\qquad 2^4 &       &=& 16 &\pmod{21},\\
    2^1 &= 2 \pmod{21}, &\qquad 2^5 &= 32   &=& 11 &\pmod{21},\\
    2^2 &= 4 \pmod{21}, &\qquad 2^6 &= 64   &=& 1  &\pmod{21}.\\
    2^3 &= 8 \pmod{21}, &           &       & &    &
}
\]
\end{document}

Aligning space characters with non-space characters with alignat

2 Answers2