# Aligning 3 equations with cases and equation number

in the equations shown below I would like to have the 'if' texts aligned - right now this does not work due to the use of three independent array environments. Thanks!!

Here is the code to generate above shown equations:

\documentclass[11pt]{scrreprt}
\usepackage[T1]{fontenc}
\usepackage[latin1]{inputenc}
\usepackage{amsmath}
\begin{document}
\begin{align}
\label{eq:RawOffsetCalculation}
y_\text{offset raw}
&
=\left\{
\begin{array}{rl}
0
&
\\
\dfrac{\sum\limits_i^{n_\text{offset}}y_\text{raw}}{n_\text{offset}}
&
\end{array}
\right. \\
\label{eq:CorrectedOffsetCalculation}
y_\text{offset corr}
&
=\left\{
\begin{array}{rl}
0
&
\\
\dfrac{\sum\limits_i^{n_\text{offset}}y_\text{corr}}{n_\text{offset}}
&
\end{array}
\right.
\\
\label{eq:CumulativeOffsetCalculation}
y_\text{offset cum}
&
=\left\{
\begin{array}{rl}
0
&
\\
\dfrac{\sum\limits_i^{n_\text{offset}}y_\text{corr cum}}{n_\text{offset}}
&
\end{array}
\right.
\end{align}
\end{document}

• Welcome to TeX.SX! You can have a look at our starter guide to familiarize yourself further with our format. – karlkoeller Jul 27 '15 at 6:59
• @Wolf277, Out of theme: You could use cases math environment for equations with cases. – juanuni Jul 27 '15 at 7:06
• Your summation notation is a bit idiosyncratic: The summation index is set to i, yet the variables being summed do not seem to contain an i-component. – Mico Jul 27 '15 at 8:04

Use the p column specifier instead of r:

\begin{array}{>{\RaggedLeft$}p{6em}<{$}l}


It needs the $..$ definition because its contents is in text mode:

\documentclass[11pt]{scrreprt}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage{amsmath}
\usepackage{array,ragged2e}
\begin{document}

\begin{align}\label{eq:RawOffsetCalculation}
y_\text{offset raw} & =\left\{
\begin{array}{>{\RaggedLeft$}p{6em}<{$}l}
\end{array} \right. \\
\label{eq:CorrectedOffsetCalculation}
y_\text{offset corr}
&
=\left\{ \begin{array}{>{\RaggedLeft$}p{6em}<{$}l}
\end{array} \right.
\\
\label{eq:CumulativeOffsetCalculation}
y_\text{offset cum} & =\left\{
\begin{array}{>{\RaggedLeft$}p{6em}<{$}l}
\end{array} \right.
\end{align}

\end{document}


• having more space between the intra-\cases lines than between the \cases entries makes them look like the last part of the first \cases is closely associated with the first part of the second one. a mixed message. – barbara beeton Jul 27 '15 at 9:13

You can use cases environment for this kind of equations. For your problem You could define multicases envinment and use phantom command to get correct alignment:

\documentclass[11pt]{scrreprt}
\usepackage[T1]{fontenc}
%\usepackage[latin1]{inputenc}
\usepackage{amsmath}

\makeatletter
\newenvironment{multicases}[1]
{\let\@ifnextchar\new@ifnextchar
\left\lbrace\def\arraystretch{1.2}%
{\endarray\right.\kern-\nulldelimiterspace}
\makeatother

\begin{document}
\begin{align}
y_\text{offset raw}&=
\begin{multicases}{1}
0,& \text{if }n_\text{offset}=0 \\
\dfrac{\sum\limits_i^{n_\text{offset}}y_\text{raw\phantom{ cum}}}{n_\text{offset}},&\text{if }n_\text{offset}>0
\end{multicases}\label{eq1}\\
y_\text{offset corr}&=
\begin{multicases}{1}
0,&\text{if }n_\text{offset}=0 \\
\dfrac{\sum\limits_i^{n_\text{offset}}y_\text{corr\phantom{ cum}}}{n_\text{offset}},&\text{if }n_\text{offset}>0
\end{multicases}\label{eq2}\\
y_\text{offset cum}&=
\begin{multicases}{1}
0,&\text{if }n_\text{offset}=0 \\
\dfrac{\sum\limits_i^{n_\text{offset}}y_\text{corr cum}}{n_\text{offset}},&\text{if }n_\text{offset}>0
\end{multicases}\label{eq3}
\end{align}
\end{document}


PS: Note label is after each equation.

Here's another solution that keeps your basic align/array setup. The desired alignment is achieved by (a) measuring the width of the largest fractional term and (b) placing the 0-terms in boxes of said width.

I would further like to suggest that you (i) insert a bit of whitespace between the three equations and (ii) indicate explicitly the dependence of the terms being summed on some index variable i. (In the code you've posted, i occurs below the summation signs but nowhere else.)

\documentclass[11pt]{scrreprt}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage{amsmath} % for "align" environment

% define the largest fractional term and save its width to "\mywid"
\newcommand\bigfrac{%
\dfrac{\sum\limits_{i=1}^{n_{\text{offset}}} y_{\text{corr\,cum},i}}{n_{\text{offset}}}}
\newlength\mywid
\settowidth\mywid{$\bigfrac$}  % save width of "\bigfrac" to "\mywid"

\begin{document}
\setcounter{chapter}{3}
\setcounter{equation}{13}
\begin{align}
y_\text{offset\,raw} &=\left\{
\makebox[\mywid][r]{$0$} %% place "0" in a box of width \mywid
& \text{if $n_{\text{offset}}=0$} \\[1.5ex]
\dfrac{\sum\limits_{i=1}^{n_{\text{offset}}}y_{\text{raw},i}}{n_{\text{offset}}}
&\text{if $n_{\text{offset}}>0$}
\end{array}\right. \label{eq:RawOffsetCalculation}\\[3ex]
y_\text{offset\,corr} &=\left\{
\makebox[\mywid][r]{$0$} %% place "0" in a box of width \mywid
& \text{if $n_{\text{offset}}=0$} \\[1.5ex]
\dfrac{\sum\limits_{i=1}^{n_{\text{offset}}}y_{\text{corr},i}}{n_{\text{offset}}}
& \text{if $n_{\text{offset}}>0$}
\end{array}\right. \label{eq:CorrectedOffsetCalculation}\\[3ex]
y_\text{offset\,cum} &=\left\{
& \text{if $n_{\text{offset}}=0$} \\[1.5ex]
& \text{if $n_{\text{offset}}>0$}