# Empty space in a aligned environment

I am attempting to align some equations using a align environment.
However it seems that when I try to make empty cells it fails to align properly

How do I properly have a empty cell in a align environment?

Here is a sample of what I am trying to do:

\documentclass{article}
\usepackage{amsmath}
\usepackage{amssymb}
\begin{document}
\begin{equation*}
\begin{aligned}
(a,1)+(b,1)                     &          &= (a+b,1) \\
((a,1)+(b,1))                   &\cdot(1,c)&= (a+b,1)\cdot(1,c) \\
(a,1)\cdot(1,c)+(b,1)\cdot(1,c) &          &= (a+b,c) \\
(a,c)+(b,c)                     &          &= (a+b,c)
\end{aligned}
\end{equation*}
\end{document}

• I'm guessing split only allows one alignment point. Perhaps you need some form of aligned. Mar 28 '17 at 18:54
• As Steven guessed you need aligned not split, if you want more that one alignment. Btw you probably need more &'s. Split only handles one single alignment. Nowadays I tend to use aligned as the goto inner env instead of split. Mar 28 '17 at 18:59
• @StevenB.Segletes Thank you for that. It seems that aligned still has a problem, albeit not a compilation error, so I have changed the question. Mar 28 '17 at 19:01
• @MöbiusStripMall -- you might benefit from looking at this question: Difference between align and alignat environments Mar 28 '17 at 21:10

While not wholly clear what you seek, this may be it, here using TABstacks.

\documentclass{article}
\usepackage{amsmath}
\usepackage{amssymb}
\usepackage{tabstackengine}
\TABstackMath
\begin{document}
\begin{equation*}
\setstackaligngap{0pt}
\TABbinary
\setstackgap{L}{1.2\baselineskip}
\alignCenterstack{
(a,1)+(b,1)                     &          &&= (a+b,1) \\
((a,1)+(b,1))                   &\cdot(1,c)&&= (a+b,1)\cdot(1,c) \\
(a,1)\cdot(1,c)+(b,1)\cdot(1,c) &          &&= (a+b,c) \\
(a,c)+(b,c)                     &          &&= (a+b,c)
}
\end{equation*}
\end{document}


Alternately, with a \tabularCenterstack instead of an \alignCenterstack, to produce the identical output:

\documentclass{article}
\usepackage{amsmath}
\usepackage{amssymb}
\usepackage{tabstackengine}
\TABstackMath
\begin{document}
\begin{equation*}
\setstacktabulargap{0pt}
\TABbinary
\setstackgap{L}{1.2\baselineskip}
\tabularCenterstack{rcl}{
(a,1)+(b,1)                     &          &= (a+b,1) \\
((a,1)+(b,1))                   &\cdot(1,c)&= (a+b,1)\cdot(1,c) \\
(a,1)\cdot(1,c)+(b,1)\cdot(1,c) &          &= (a+b,c) \\
(a,c)+(b,c)                     &          &= (a+b,c)
}
\end{equation*}
\end{document}


Solution with array:

\documentclass{article}
\usepackage{amsmath}
\usepackage{amssymb}
\begin{document}
$\setlength\arraycolsep{1pt} \begin{array}{r@{}cl} (a,1)+(b,1) & &= (a+b,1) \\ ((a,1)+(b,1)) &{}\cdot{}(1,c)&= (a+b,1)\cdot(1,c) \\ (a,1)\cdot(1,c)+(b,1)\cdot(1,c) & &= (a+b,c) \\ (a,c)+(b,c) & &= (a+b,c) \end{array}$
\end{document}

• Check the spacing around the \cdot. Mar 28 '17 at 19:03
• ups, corrected! Mar 28 '17 at 19:05

\documentclass{article}
\usepackage{amsmath}
\usepackage{amssymb}
\begin{document}
aligned
\begin{equation*}
\begin{aligned}
(a,1)+(b,1)                     &          &&= (a+b,1) \\
((a,1)+(b,1))                   &\cdot(1,c)&&= (a+b,1)\cdot(1,c) \\
(a,1)\cdot(1,c)+(b,1)\cdot(1,c) &          &&= (a+b,c) \\
(a,c)+(b,c)                     &          &&= (a+b,c)
\end{aligned}
\end{equation*}

alignat
\begin{alignat*}{2}
(a,1)+(b,1)                     &          &&= (a+b,1) \\
((a,1)+(b,1))                   &\cdot(1,c)&&= (a+b,1)\cdot(1,c) \\
(a,1)\cdot(1,c)+(b,1)\cdot(1,c) &          &&= (a+b,c) \\
(a,c)+(b,c)                     &          &&= (a+b,c)
\end{alignat*}

\end{document}