Increasing the size of parentheses

Question

\begin{equation}
\begin{split}
G^{2} = &-2 \{ \sum_i \sum_j \sum_k z_{ijk111}\log \{ \frac{m_{ijk}}{z_{ijk111}}\}
               +  \sum_j\ \sum_k z_{+jk211} \log \{ \frac{\sum_i m_{ijk}a_{ijk}}{z_{+jk211}} \}
               +  \sum_k\ \sum_i z_{i+k121} \log \{ \frac{\sum_j m_{ijk}b_{ijk}}{z_{i+k121}} \} \\
        &\quad + \sum_j \sum_i z_{ij+112} \log \{ \frac{\sum_km_{ijk}b_{ijk}}{z_{ij+112}} \}
               + z_{+++222} \log \{ \frac{m_{ijk}a_{ijk}b_{ijk}c_{ijk}\theta_{M_{(I)}}\theta_{M_{(J)}}\theta_{M_{(K)}}}{z_{+++222}} \}
             \} 

\end{split}
\end{equation}

The parenthesis after -2 is small, I want it larger. I am also having problem with making larger parenthesis specially after log. Any solutions?

Answer 1

For equations such as the one you're looking to typeset, it's usually best not to rely on any automatic sizing of "fences" (i.e., round parentheses, square brackets, curly braces, etc). Instead, use the TeX/LaTeX \big, \Big, \bigg, and \Bigg directives to size the fences. For the equation at hand, \bigg for both the outermost curly braces and for the inner fences seems OK.

I would further recommend (i) splitting the equation (a log-likelihood function, right?) across three lines instead of just two so give it a chance of fitting inside the text block, and (ii) using different fence symbols for the inner fences -- which enclose the arguments of the various logarithm terms -- and the outer fences. In the example below, I use round parentheses for the inner fences. Oh, and you also seem to be inserting "thin spaces" (\,) between some summation symbols but not between others; I wouldn't insert any such thin-spaces.

\documentclass{article}
\usepackage[margin=1in]{geometry}  % choose whatever margins suit you best
\usepackage{amsmath} % amsmath package provides 'split' environment
\begin{document}
\begin{equation}
\begin{split}
G^{2} = -2 \bigg\{& 
\sum_i\sum_j\sum_k z_{ijk111}\log \biggl( \frac{m_{ijk}}{z_{ijk111}}\biggr) + 
\sum_j\sum_k z_{+jk211}\log \biggl( \frac{\sum_i m_{ijk}a_{ijk}}{z_{+jk211}}\biggr)\\
&+ \sum_k\sum_i z_{i+k121}\log \biggl( \frac{\sum_j m_{ijk}b_{ijk}}{z_{i+k121}} \biggr) 
 + \sum_j\sum_i z_{ij+112}\log \biggl( \frac{\sum_km_{ijk}b_{ijk}}{z_{ij+112}} \biggr) \\
&+ z_{+++222} \log \biggl( \frac{m_{ijk}a_{ijk}b_{ijk}c_{ijk}\theta_{M_{(I)}}\theta_{M_{(J)}}\theta_{M_{(K)}}}{z_{+++222}} \biggr)
\bigg\} 
\end{split}
\end{equation} 
\end{document}

Answer 2

\begin{equation}
\begin{split}
G^{2} &= -2 \Biggl\{ \sum_i \sum_j \sum_k z_{ijk111}\log \left\{ \frac{m_{ijk}}{z_{ijk111}}\right\}
 + \ \sum_j\ \sum_k z_{+jk211} \log \left\{ \frac{\sum_i m_{ijk}a_{ijk}}{z_{+jk211}} \right\} + \ \sum_k\ \sum_i z_{i+k121} \log \left\{ \frac{\sum_j m_{ijk}b_{ijk}}{z_{i+k121}} \right\} \\
& + \ \sum_j\ \sum_i z_{ij+112} \log \left\{ \frac{\sum_km_{ijk}b_{ijk}}{z_{ij+112}} \right\}
+z_{+++222} \log \left\{ \frac{m_{ijk}a_{ijk}b_{ijk}c_{ijk}\theta_{M_{(I)}}\theta_{M_{(J)}}\theta_{M_{(K)}}}{z_{+++222}}\right\}\Biggr\} 
\end{split}
\end{equation}

You can choose the dimension of your brackets using the following commands(in order of dimension from smaller ones to bigger ones): \bigl-\bigr, \Bigl-\Bigr, \biggl-\biggr, \Biggl-\Biggr.