Csdrhrt

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,} &quadtext{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,} &quadtext{En caso contrario}

         end{cases}\

    $y_{j}$ = 

         &begin{cases}

           text{1,} &quadtext{  Si se construye planta en el sitio j ( j $in $   {1,2,3,4,5,6,7})} \

           text{0,} &quadtext{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,} &quadtext{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,} &quadtext{En caso contrario}

     end{cases}

]

[   

y_{j} = 

     begin{cases}

       text{1,} &quadtext{  Si se construye planta en el sitio j ( j $in $   {1,2,3,4,5,6,7})} \

       text{0,} &quadtext{En caso contrario}

     end{cases}

]





end{document}

and I want they are aligned, like this

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 $i$ ($iin{1,2,3,4,5,6,7,8,9,10}$) \

      a sitio $j$ ($jin{1,2,3,4,5,6,7}$)

      end{tabular} \[4ex]

  0, &text{En caso contrario}

end{cases}\

y_{j} &=

  begin{cases}

  1, &text{Si se construye planta en el sitio $j$ ($jin{1,2,3,4,5,6,7}$)} \[1ex]

  0, &text{En caso contrario}

  end{cases}

end{align*}



end{document}

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} 

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,} &quadtext{Si se envía agua desde área $i$ ($i in {1,2,dots,10}$) a sitio $j$ ($j in {1,2,dots,7}$)} \

text{0,} &quadtext{En caso contrario}

end{cases}\

y_{j} &= 

begin{cases}

text{1,} &quadtext{  Si se construye planta en el sitio $j$ ($j in {1,2,dots,7}$)} \

text{0,} &quadtext{En caso contrario}

end{cases}

end{align*}

end{document}

Output: