4

I have problem with my piecewise functions

I read others post and I tried this but I have errors

\documentclass{article}
\usepackage{amsmath}
\begin{document}
    \begin{align*}
    $x_{{i}{j}}$ = 
         &\begin{cases}
           \text{1,} &\quad\text{Si se envía agua desde área i ( i $\in$   \{1,2,3,4,5,6,7,8,9,10\}) a sitio j ( j $\in$  \{1,2,3,4,5,6,7\})} \\
           \text{0,} &\quad\text{En caso contrario}
         \end{cases}\\
    $y_{j}$ = 
         &\begin{cases}
           \text{1,} &\quad\text{  Si se construye planta en el sitio j ( j $\in $   \{1,2,3,4,5,6,7\})} \\
           \text{0,} &\quad\text{En caso contrario}
         \end{cases}
    \end{align*}
\end{document}

Runaway argument? ! Paragraph ended before \align* was complete. \par l.592

I did this (using [) and it works well but they appear not aligned

\documentclass{article}
\usepackage{amsmath}
\begin{document}
\[   
x_{{i}{j}} = 
     \begin{cases}
       \text{1,} &\quad\text{Si se envía agua desde área i ( i $\in$   \{1,2,3,4,5,6,7,8,9,10\}) a sitio j ( j $\in$  \{1,2,3,4,5,6,7\})} \\
       \text{0,} &\quad\text{En caso contrario}
     \end{cases}
\]
\[   
y_{j} = 
     \begin{cases}
       \text{1,} &\quad\text{  Si se construye planta en el sitio j ( j $\in $   \{1,2,3,4,5,6,7\})} \\
       \text{0,} &\quad\text{En caso contrario}
     \end{cases}
\]


\end{document}

enter image description here

and I want they are aligned, like this

enter image description here

  • remove the $$ around x_{ij} and y_{j}. \begin{align*} is already a math environment. – Troy Nov 30 '18 at 17:00
  • lol I did that and it didn't work before but now it works hahaha thanks man!! is there a way to align the functions using [ .... ] ? – EmiliOrtega Nov 30 '18 at 17:02
  • Yes, with the \begin{aligned} environment from amsmath. E.g. of its use: Alignment in equations – Troy Nov 30 '18 at 17:04
3

Beware! align already typesets its contents in math mode (but \text reverts to text mode).

You have to just align the equals signs with &=; for the long line, I suggest a tabular. Some vertical spacing will help, too.

\documentclass{article}
\usepackage{amsmath}
\begin{document}

\begin{align*}
x_{ij} &=
  \begin{cases}
  1, &\begin{tabular}[t]{@{}l@{}}
      Si se envía agua desde área $i$ ($i\in\{1,2,3,4,5,6,7,8,9,10\}$) \\
      a sitio $j$ ($j\in\{1,2,3,4,5,6,7\}$)
      \end{tabular} \\[4ex]
  0, &\text{En caso contrario}
\end{cases}\\
y_{j} &=
  \begin{cases}
  1, &\text{Si se construye planta en el sitio $j$ ($j\in\{1,2,3,4,5,6,7\}$)} \\[1ex]
  0, &\text{En caso contrario}
  \end{cases}
\end{align*}

\end{document}

enter image description here

2

Here it is I simplified the text part typing using the cases* environment from mathtols (needless to load àmsmath`). I had to dplit the first case to make it fit the margins:

\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage[showframe]{geometry}
\usepackage{mathtools}

\begin{document}

    \begin{align*}
    x_{{i}{j}} & =
         \begin{cases*}
           \text{1,} &\quad Si se envía agua desde área $ i\: ( i \in \{1,2,3,4,5,6,7,8,9,10\})$ \\
             & \quad a sitio $ j\: ( j \in \{1,2,3,4,5,6,7\})$ \\
           \text{0,} &\quad{En caso contrario}
         \end{cases*}\\[1.5ex]
   y_{j} & =
   \begin{cases*}
 1, &\quad Si se construye planta en el sitio $ j\: ( j \in \{1,2,3,4,5,6,7\})$ \\
 0, &\quad En caso contrario
 \end{cases*}
    \end{align*}

\end{document} 

enter image description here

1

If we go back to your original attempt, a few quick changes gives the result you wanted. This: removes the $$ around x_{ij} and y_j and moves the & you use for alignment to align the equals signs. Edit: I also compressed the set notation to shorten the long line and returned i and j to math mode, as you currently have them as subscripts in math mode. If you'd prefer them to be set upright you should change the subscripts as well.

\documentclass{article}
\usepackage{amsmath}
\begin{document}
\begin{align*}
x_{ij} &=
\begin{cases}
\text{1,} &\quad\text{Si se envía agua desde área $i$ ($i \in \{1,2,\dots,10\}$) a sitio $j$ ($j \in \{1,2,\dots,7\}$)} \\
\text{0,} &\quad\text{En caso contrario}
\end{cases}\\
y_{j} &= 
\begin{cases}
\text{1,} &\quad\text{  Si se construye planta en el sitio $j$ ($j \in \{1,2,\dots,7\}$)} \\
\text{0,} &\quad\text{En caso contrario}
\end{cases}
\end{align*}
\end{document}

Output: New aligned output

  • Since i and j are used in math mode on the LHS, it seems appropriate to use $i$ ($i \in \{1,\dots,10\}$) and $j$ ($j \in \{1,\dots,7\}$) on the RHS. – Werner Nov 30 '18 at 17:17
  • Good point, as is the compression of the set notation. Edits made. – aoi Nov 30 '18 at 17:30

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.