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I'm trying to do some sort of global alignment for my equations and didn't succeed to find anything online. More precisely, my cases environment inside my aligned and equation* has its own & alignment-symbols that I want to be working with other ones inside aligned. Hopefully this MWE (using amsmath) makes it understandable:

\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage{amsmath}

\begin{document}

\begin{equation*}
\begin{aligned}
                    & \left| f_{(x)} \right| &\overset{!}{\leq} &L \left| x - y \right| &                      \\
    \Leftrightarrow & \left| x - y \right|   &\leq              &L \left| x - y \right| &                      \\
    \Leftrightarrow & \begin{cases}
                      x - y                  &\leq              &L (x - y)              &\text{ for } x \geq y \\
                      y - x                  &\leq              &L (y - x)              &\text{ for } x > y    \\
                      \end{cases}                                                                              \\
\end{aligned}
\end{equation*}

\end{document}

How do I align every part over each other like the &s in the code above?

Thank you for any hints. I'm also happy for feedback on my code-style :)

Extra question: Why do I get an "Extra alignment tab has been changed to \cr." and an "underfull hbox" at the very end?

Similar questions not answering mine:

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  • It's not quite a MWE. A MWE is to be typeset "out of the box", so it must have \documentclass{}, the necessary packages, \begin{document} and so on…
    – Franck Pastor
    Dec 16, 2017 at 14:00
  • @FranckPastor done, thanks for pointing out!
    – 4ster
    Dec 16, 2017 at 14:54
  • 1
    The cases environment defines a box of its own IIRC, so I can't see how it can be managed this way. By the way, this environment doesn't accept more than one ampersand per line, so your code can't be typeset as it is.
    – Franck Pastor
    Dec 16, 2017 at 15:20
  • Methinks you are trying too align too much. Is that really necessary?
    – Harald Hanche-Olsen
    Dec 16, 2017 at 16:02
  • @FranckPastor, again, thank you. That will probably mean that I'm dropping the use of cases then and have to go for doing it by myself...
    – 4ster
    Dec 16, 2017 at 17:53

2 Answers 2

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enter image description here

\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage{amsmath}

\begin{document}

\begin{equation*}
\begin{alignedat}{3}
                    && | f_{(x)}| &\overset{!}{\leq} L | x - y | &                      \\
    &{\Leftrightarrow} & | x - y | &\leq          L | x - y | &                      \\
    &\smash{\raisebox{-8pt}{$\Leftrightarrow\biggl\{$}}
                    &  x - y    &\leq   L (x - y)   &\text{ for } x \geq y \\
                     &&y - x     &\leq   L (y - x)   &\text{ for } x > y                          
\end{alignedat}
\end{equation*}

\end{document}
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4
  • Wow this just looks perfect as imagined. After reading about alignedat and learning about cases only supporting one ampersand, I guess doing it all manually is the only option. However, and don't get me wrong on this, I really don't like raisebox and biggl\{ instead of dynamical parantheses like \left\{. I guess nesting two multline boxes will be the way to go...
    – 4ster
    Dec 16, 2017 at 18:00
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    @4ster it's almost always better to choose the size than use left/right eg uses such as \left| x - y \right| should be avoided.
    – David Carlisle
    Dec 16, 2017 at 18:03
  • that's interesting to hear. I thought keeping everything variable (e.g. allowing to change the documents font size) was a good measure to take - 8pt in your code didn't seem to comply with that approach. Now I guess I need a good guide for LaTeX-style to change my approach. With your experience, can you recommend something where I can get a deeper understanding of this?
    – 4ster
    Dec 16, 2017 at 18:48
  • 1
    @4ster see tex.stackexchange.com/q/173717/1090
    – David Carlisle
    Dec 16, 2017 at 19:23
2

With some gentle persuasion applied to bigdelim:

\documentclass{article}
\usepackage{amsmath}
\usepackage{array,bigdelim}
\usepackage{etoolbox}

\newcommand{\Nleq}{\overset{!}{\leq}}

\makeatletter
\newcommand{\reducedelim}{%
  \patchcmd{\@ldelim}{\multirow@dima}{0.75\multirow@dima}{}{}%
}
\makeatother

\begin{document}

\begin{equation*}
\renewcommand{\arraystretch}{1.5}
\setlength{\arraycolsep}{0pt}
\begin{array}{ l r >{{}}c<{{}} l @{\qquad} l }
   & \lvert f_{(x)} \rvert &\Nleq& L \lvert x - y \rvert \\
\Leftrightarrow
   & \lvert x - y \rvert  &\leq&  L \lvert x - y \rvert \\
\reducedelim\ldelim\lbrace{2}{*}[$\Leftrightarrow$\qquad]
   & x - y                 &\leq&  L (x - y) &\text{for $x \geq y$} \\
   & y - x                 &\leq&  L (y - x) &\text{for $x > y$}
\end{array}
\end{equation*}

\end{document}

enter image description here

On the other hand, the middle inequality is satisfied, for all x and y, if and only if L ≥ 1.

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