# why aren't the \left and \right before my parentheses changing their size?

I am working on a document, and in only one case have the \left and \right before my parentheses seemed to do anything. For example, I have this equation:

$$\mathbb{E}(RS_{nd}) = (1-F(p_k + g^*(\tau, k\tau)))^{k-1}\left(\left(\left(1-PR[S]\right)+PR[S]\left(1-F\left(\hat{p}_k\right)\right)\right)\left(p_k-c\right)\right)$$

and it produces this output

Why aren't the parenthesis displayed in different sizes? I am sorry for the long equation -- it seems to be mostly a problem in my longer equations. All the parentheses seem to match up with each other. Any ideas? T

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\left and \right adjust in size to fit their content. Each of your expressions (appear as though they) are the same size, so there is no need for the () to adjust their size –  cmhughes Jan 10 '12 at 3:27
it's really not a great idea to put \left and \right on the innermost delimiters when what's inside isn't larger than the base size. the last \left(p\_k-c\right) is one example of this. –  barbara beeton Jan 10 '12 at 13:37
@barbarabeeton: Apart from being unnecessary, is there any problem with it? –  celtschk Jan 10 '12 at 17:28
@celtschk -- if \left and \right are always properly matched, there shouldn't be any problem in the output. but if the file has to be edited for any reason, extra care has to be taken to make sure that nothing becomes unbalanced. this could definitely cause headaches for the production staff (and possibly introduce errors) if a file is submitted to and accepted for publication in a journal. –  barbara beeton Jan 10 '12 at 20:08

Because the interior expressions are not larger than the default size. If you want to use enlarged parentheses in this way, you might try \bigl(...\bigr) and its cousins with \Big, \bigg, and \Bigg. Though some might say that for readability, you should also use different types of delimiters.

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Normally TeX stretches \left and \right to be just a bit shorter than the contained content to avoid stuff exploding too much, but for this kind of expression you probably want it to expand to be a a bit bigger, to make delimiters at least 10% bigger than the content add

\delimiterfactor=1100


eg in the document preamble

which is a bit much, but you can reduce to taste

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You mean the internet has been lying to me all these years about needing \bigl? –  Ryan Reich Jan 10 '12 at 19:36
xkcd.com/386 –  David Carlisle Jan 12 '12 at 16:48