[Tex/LaTex] Multiple aligning symbols

align

I would like to do the closest thing there is to opening an align* environment inside another align* environment. In other words: it would be great if there were an environment, call it Align, that allows you to use to symbols to align equations in math mode using a specified number of aligning symbols &1, &2, …, &n. For example something that works like this:

\begin{Align*}[2] &1 1=1 \\ &1 4 &2= 2+2 \\ &2 = 1+1+1+1 \\ &1 7 = 7 \end{Align*}

which I would want to look like

1 = 1
4 = 2+2 =
  = 1+1+1+1
7=7

Does there exist such an environment?

I tried looking in this guide but I couldn't find anything, and I'm just a beginner… thanks for any help!

Best Answer

If you only have a single alignment position, a regular align would suffice. For multiple alignment positions, use alignat:

\documentclass{article}
\usepackage{amsmath}% http://ctan.org/pkg/amsmath
\begin{document}
\begin{alignat*}{3}
  1 &= 1             \\
  4 &= 2+2     & &=  \\
    &= 1+1+1+1 & &=4 \\
  7 &= 7
\end{alignat*} 
\end{document}

enter image description here

The alignat environment allows you to specify the number of alignment positions.

Herbert's mathmode document provides some informative examples on the different amsmath environments and usage. Specifically, see Part II amsmath package (p 43). An example of your output request is on p 46.

Related Solutions

[Tex/LaTex] Spurious space above align environment at top of page/minipage

The alignment environments of amsmath are not designed to be at the start of a paragraph. While this can be acceptable in normal situations, this has bad effects when we use a minipage for typesetting an alignment at a reduced width.

The minipage problem can be solved by patching the \start@align command (and also \start@gather and \start@multline) with

\usepackage{etoolbox}
\makeatletter
\pretocmd\start@align{%
  \if@minipage\kern-\topskip\kern-\abovedisplayskip\fi
}{}{}
\makeatother

This exploits the fact that at the start of a minipage the conditional \if@minipage is true, but upon starting a paragraph it becomes false, so subsequent align environments in the same minipage won't be affected.

There is a similar patch for "curing" the environments at start-of-paragraph, but I'm somewhat reluctant to show it, as I believe that a paragraph should never start with a displayed equation (with the above mentioned exception).

[Tex/LaTex] Multiple \cline{x-y} in align environment for subtracting equations

I'd use a simple array environment:

\documentclass{article}
\usepackage{amsmath}

\begin{document}
\[\arraycolsep=1.4pt\def\arraystretch{1.3}
\begin{array}{rcr p{1cm} rcr} 
    12a + 4b + c  &=& -3    &&     12a + 2b  &=&  0 \\
   -27a - 6b - c  &=&  0    &&    -15a - 2b  &=& -3 \\
    \cline{1-3} \cline{5-7}
    -15a - 2b \phantom{\,-\,c\,} &=& -3  & &     -3a  \phantom{\,-\,2b\,} &=& -3  \\
                           & &      &&                     a  &=& -1  
\end{array}
\]

\end{document}

enter image description here

For the arrow you can define two nodes with TikZ or PSTricks.

Best Answer

Related Solutions

[Tex/LaTex] Spurious space above align environment at top of page/minipage

[Tex/LaTex] Multiple \cline{x-y} in align environment for subtracting equations

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