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This question already has an answer here:

Why does f\left(x\right) result in more space before the ( than f{\left(x\right)}?

i.e. Why does putting extra braces suppress the space?

marked as duplicate by egreg, Svend Tveskæg, Mehrdad, Peter Jansson, Sean Allred Feb 23 '14 at 23:18

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  • I'm not sure why it does that but for your particular example, you should just use f(x). – Svend Tveskæg Feb 23 '14 at 21:56
  • @SvendTveskæg: That comment completely missed the point of my question. – Mehrdad Feb 23 '14 at 21:57
  • With the braces, the mathematical properties (\mathrel, \mathop, etc.) of the parens are lost outside the braces. Similar to $a - b$ versus $a {- b}$. – Steven B. Segletes Feb 23 '14 at 21:57
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    @Mehrdad I don't think that typing $f\left(\frac{1}{2}\right)$ would have been so far from minimal and it would have better explained the issue. Why are you taking it so personally? – egreg Feb 23 '14 at 22:16
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    @Mehrdad I think you actually missed the point of the comments, which is, in fact, comment. If someone asks why {\it sniff} and cry eats some space between sniff and and he will probably get some comments asking why isn't he using \textit{sniff} (which, in my opinion, are beneficial), rather than explaining the italic correction (that would probably be an answer). In short: “I really freaking hate comments like yours”. – Manuel Feb 23 '14 at 22:27
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\left and \right create a "inner formula" with additional spaces around except in scriptsize or smaller or after an opening delimiter or before a closing delimiter. The curly braces put the inner formula into a sub formula with the same spacing rules as an ordinary math atom (\mathord).

See package mleftright, if you want a solution without additional spacing:

\documentclass{article}
\usepackage{mleftright}
\begin{document}
\[
  f \left(\frac xy\right) g =
  f {\left(\frac xy\right)} g =
  f \mleft(\frac xy\mright) g
\]
\end{document}

Result

  • I'm asking why one would use \left and \right there. – egreg Feb 23 '14 at 22:02
  • @egreg: That's the disadvantage of a minimal example. The size of the argument does not matter for the horizontal spacing. In real life x could be a larger construct like a fraction or whatever. – Heiko Oberdiek Feb 23 '14 at 22:04
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    That's clear; but I see too many people using \left and \right when they shouldn't. – egreg Feb 23 '14 at 22:05
  • @HeikoOberdiek: Thank you, this is a great answer. +1 – Mehrdad Feb 23 '14 at 22:12

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