2

This question already has an answer here:

I would like to use the sum sign in an conditional expression. There is no error message but the Fz is supposed to be under the sum sign but instead its a subscript. Can someone help me solving my problem?

\begin{equation}  
X = \left\{  
\begin{array}{ll}  
q_{B} = \sum_{Fz}\left(WT_{Fz}  & , \textnormal{ if } q_{B} > 1800 * N_{FS} \\  
q_{S} = \sum_{Fz}\left(WT_{Fz}  & , \textnormal{ if } q_{B} \leq 1800 * N_{FS}\\  
\end{array}  
\right.  
\end{equation}

marked as duplicate by Werner equations Sep 4 '16 at 13:58

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  • 1
    Welcome to TEX.SX. Could you please put a compilable minimal working example to reproduce the problem you face? – Diaa Sep 4 '16 at 12:36
  • I would see the solution given by Peter for tex.stackexchange.com/questions/3262/… – stephematician Sep 4 '16 at 12:38
  • Essentially you're trying to achieve a \displaystyle output for something set in\textstyle. – Werner Sep 4 '16 at 13:57
2

Crystal ball suggests that you might be looking for this:

% My standard header for TeX.SX answers:
\documentclass[a4paper]{article} % To avoid confusion, let us explicitly 
                                 % declare the paper format.

\usepackage[T1]{fontenc}         % Not always necessary, but recommended.
% End of standard header.  What follows pertains to the problem at hand.

\usepackage{mathtools}



\begin{document}

Some text.
\begin{equation}
    X = \begin{dcases*}  
        q_{B} = \sum_{Fz} WT_{Fz},  & if $q_{B} > 1800 * N_{FS}$; \\  
        q_{S} = \sum_{Fz} WT_{Fz},  & if $q_{B} \leq 1800 * N_{FS}$ \\  
    \end{dcases*}  
\end{equation}

\end{document}

Output:

Output of the code

1

This works:

\documentclass{article}

\usepackage{amsmath}

\begin{document}

\begin{equation}  
X = \begin{cases}   
q_{B} = \sum\limits_{Fz} WT_{Fz}  & , \textnormal{ if } q_{B} > 1800 * N_{FS}, \\  
q_{S} = \sum\limits_{Fz} WT_{Fz}  & , \textnormal{ if } q_{B} \leq 1800 * N_{FS}.\\  
\end{cases}  
\end{equation}


\end{document}

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