9

I'm trying to use \cdotas a dummy for a function argument in the following expression

C(\cdot\mid\mathcal{F}_{t-1}) 

However, the above produces more space to the right of the dot than to the left. I'd like the spacing to be symmetrical. I've tried using {}on either side but haven't been able to get the desired result.

  • This question is quite similar. Maybe it answers your question too. – hbaderts Aug 17 '15 at 8:45
  • 1
    The trouble is not with \cdot but with \mid, which is a relation. You would get equal (but small) spacing using {\mid}, but I wouldn't suggest that. Isn't C(\,\cdot\mid\mathcal{F}_{t-1}) enough? – campa Aug 17 '15 at 8:45
  • That is better but still not perfectly symmetrical. Perhaps it would be better to use an alternative to \mid that isn't a relation. I'm just not sure such a thing exists. – user2249626 Aug 17 '15 at 8:48
16

Since you want to use the blank next either between an opening atom (the open parenthesis) and a relation atom (\mid) or between a relation atom and a closing atom, you can define \blank to be a relation symbol:

\documentclass{article}

\newcommand{\blank}{\mathrel{\;\cdot\;}}

\begin{document}

$C(\blank \mid F_{t-1})$

$C(x \mid \blank)$

\end{document}

The trick is that TeX doesn't add space in cases

Open Rel Rel

or

Rel Rel Close

enter image description here

  • If \blank is to be used in a different context, such as “blank+x”, then {\blank}+x should do. – egreg Aug 17 '15 at 9:10
  • Why not just make the widened \cdot an ord here? Then it would be in the same category as x. – Andrew Swann Aug 20 '15 at 12:10
  • @AndrewSwann The spacing would be asymmetric. It would be right if instead of \mid a comma was used. – egreg Aug 20 '15 at 15:12

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