delimitersmath-mode
I have an equation contained inside \[...\], which automatically makes a \sum with sub- and superscripts turn big–so that the summation sign looks awkward inside parenthesis. Any idea how to make the parenthesis completely enclose the whole summation?
\documentclass{article}
\begin{document}
We have:
\[ \sum_{i=1}^n i = (\sum_{i=1}^{n-1} i) + n =
\frac{(n-1)(n)}{2} + n = \frac{n(n+1)}{2} \]
\end{document}
The ams parenthesis of specific size are typeset by using \left and \right and putting in an invisible "thing" of a certain height to ensure that they are big enough. Mimicking that, you could do: \left(\rule{0cm}{2cm}\right. to get a left parenthesis of 2cm height. Note that the AMS command also adds a little horizontal space which you might need to put in as well. If you do this often, you could easily define new sizes:
\makeatletter
\newcommand{\vast}{\bBigg@{4}}
\newcommand{\Vast}{\bBigg@{5}}
\makeatother
Then in your document:
\[
\Vast( \frac{\prod_0^\infty k}{\sum_0^\infty n} \Vast)
\]
produces:
I recommend also taking a look at Vertically asymmetric size variation for parentheses about vertically centring parentheses.
(Note I've assumed that you're using amsmath since you tag it with amsmath and the commands \big and so forth are ones that amsmath produces. If you're using a different package to get these commands, then this solution won't work.)
This is another case showing that automatic resizing with \left and \right should be used with care. It gives unwanted spaces in some cases and wrong results in others like this.
The best thing I can suggest you is to avoid \left and \right for this command or at least to use the facilities offered by mathtools.
For example, you could define
\usepackage{amssymb,mathtools}
\newcommand{\shat}[1]{\vphantom{#1}\smash[t]{\hat{#1}}}
\DeclarePairedDelimiter{\Ex}{[}{]}
\newcommand{\E}{\mathbb{E}\Ex}
so that
$\E{A}$
$\E{\hat{A}}$
$\E{\frac{A}{2}}$
$\E*{\frac{A}{2}}$
$\E*{\dfrac{A}{2}}$
will give the following result (\left and \right are applied only when the you call \E* instead of \E):
One can also specify explicit size of the brackets with an optional argument:
$\E[\big]{\hat{A}}$
will produce slightly bigger brackets than $\E{A}$.
Best Answer
The usual thing to do is replace
(with\left(and)with\right), which automatically expand to fit the material between them. Note that every\left...requires a\right...(but the type of bracket may be different, i.e.\left(...\right]also works).I would typeset your equation as
For manual control of sizes (most of the time you won't need these)
produce