[Tex/LaTex] “(” or “\left(” parentheses

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What is the difference between ( and \left( in LaTeX? Sometimes, when the content is small, it does not seem to matter which pair I use.

What is the best practice when it comes to which parentheses use?

Best Answer

There are in fact four important differences:

  1. \left( ... \right) etc. scales according to the height and depth of its contents. This scaling is "dumb" in the sense that it will always take the full height and depth into account (how much of the expression is covered is controlled by \delimitershortfall and \delimiterfactor): for example, in \left( \rule{1cm}{1cm} \right), the parentheses reach far below the square. A more relevant example is \left( \sum_a^b \right) where the parentheses also cover the sum limits. The simple delimiters ( and ) and also the manually-sized delimiters \big( etc. don't scale.
  2. \left ... \right forms a group: if you say \newlength\mylength \[ \left( \mylength=1cm \right) \the\mylength \] you get 0.0pt because the value was reset. More importantly, you cannot have line breaks inside \left ... \right groups, neither manual nor automatic ones, without special trickery. Any \left needs a matching \right.
  3. Some characters produce different glyphs when being applied to \left etc. For example, < produces a less-than sign, while \left< produces an angle bracket. \big etc. use the same interpretation as \left (because they use \left internally). Technically, \left uses the delimiter code, while unadorned characters use the mathematical code.
  4. The spacing is different. Technically, \left ... \right inserts an inner node, while ( inserts an opening node. This becomes visible in $\sin()$ vs. $\sin\left(\right). Therefore you can never simply replace ( by \left( and vice versa, you always have to check whether the spacing comes out right. An automatic solution to this issue is offered in Spacing around \left and \right, but the spacing within \left...\right can still be different as explained in this answer.
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