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How can I write in MathJax a circle with a bullet inside it? I know \odot, but this is a circle with a dot inside it; I want most of the circle be filled by the dark circle inside and only a thin clear rim surrounding it.

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    $\begingroup$ $\bigodot\kern-0.975em\bullet$ which lends itself to $$\Large\stackrel{\bigodot\kern-0.975em\bullet\bigodot\kern-0.975em\bullet}{\Huge\smile}$$ $\endgroup$
    – Asaf Karagila Mod
    Feb 9 at 20:54
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    $\begingroup$ The bullet isn't quite centered, @Asaf ;P Seriously though, nice work $\endgroup$
    – amWhy
    Feb 9 at 20:58
  • $\begingroup$ Smiley is looking to her left! $\endgroup$
    – amWhy
    Feb 9 at 20:59
  • $\begingroup$ @AsafKaragila if I add "\Large" to \bullet, the resulting larger bullet is not in the center? $\endgroup$
    – Zuhair
    Feb 9 at 21:00
  • $\begingroup$ @Asaf, The problem is that its not perfectly centered. $\endgroup$
    – Zuhair
    Feb 9 at 21:09
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    $\begingroup$ @Zuhair Adjust the kerning to your taste: $\bigodot\kern-0.9em\bullet \quad \bigodot\kern-0.8em\bullet \quad \bigodot\kern-0.7em\bullet \quad \bigodot\kern-0.96em\bullet \quad \bigodot\kern-0.5em\bullet$ (these run from -0.9em to -0.5 em) $\bigodot\kern-0.835em\bullet$ $\bigodot\kern-0.835em\bullet$ looks okay to me... $\endgroup$
    – Xander Henderson Mod
    Feb 9 at 21:18
  • $\begingroup$ @Xander Is .835 the fourth from the left? That looks pretty centered, more or less, in terms of horizontally. $\endgroup$
    – amWhy
    Feb 9 at 22:21
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    $\begingroup$ Out of curiosity, what mathematical operation is this going to represent? Has it been found or used in other books/papers/PDFs? $\endgroup$ Feb 9 at 23:23
  • $\begingroup$ Surprisingly, even $\require{enclose}\enclose{circle}{\bullet}$$\require{enclose}\enclose{circle}{\bullet}$ doesn't look great (which I found from here $\endgroup$ Feb 10 at 7:30
  • $\begingroup$ @amWhy I don't think so. I believe that the last one (which is not in the group with the others) is -0.835em. $\endgroup$
    – Xander Henderson Mod
    Feb 10 at 13:51
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    $\begingroup$ @SarveshRavichandranIyer on a quick google, I only saw that its used as a fancy bullet on some twitter posts, some Thai tourism site, and an engineering book. In the case of OP, Zuhair has been exploring the idea of creating new notation link1 (Math.SE), link2. (MO). $\endgroup$ Feb 12 at 3:08

1 Answer 1

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In Mathjax, it is hard to overlay characters and get them perfectly aligned on all screens. ($\rm\LaTeX$ has purpose-built packages.) Instead, you can use the following Unicode character (which Mathjax allows):

⦿
CIRCLED BULLET
Unicode: U+29BF, UTF-8: E2 A6 BF

$$a⦿b. ⦿^{⦿^{⦿^{⦿}}}.\Huge ⦿.$$ gives $$a⦿b. ⦿^{⦿^{⦿^{⦿}}}.\Huge ⦿.$$ It even comes with the spacing of a binary operator, $a⦿b$ $a{⦿}b$$a⦿b$ $a{⦿}b$

Here's a screenshot of the above using two different renderers, HTML-CSS (with my preinstalled XITS font):

enter image description here

and common HTML:

enter image description here

If you don't want to copy-paste and have good memory, one can type \unicode{x29bf}$\unicode{x29bf}$ for the same effect. (This works for other Unicode symbols, e.g. \unicode{x1D7D9}$\unicode{x1D7D9}$. I am both lazy and forgetful, so I use software.)

  • Some other circled Unicode symbols: $⊕⊖⊗⊘⊙⊚⊛⊜⊝⨀⨁⨂⨷⨸⦶⦷⦸⦹⦺⦻⦼⦽⦾⦿⧀⧁$.
  • I couldn't find a big version to make the equivalent of $⨀\limits_a^b$$⨀\limits_a^b$, but Davide Cervone in the comments below has given the following beautiful suggestion (copied verbatim)

You might consider \mathop{\vcenter{\huge ⦿}}_{n=1}^{\infty} as more semantic and a little easier to use, plus it centers the operator, and \limits will work with that: $$\mathop{\vcenter{\huge ⦿}}_{n=1}^{\infty} abc$$ Even better might be \mathop{\vcenter{\huge\unicode[.67,.15]{x29BF}}}_{n=1}^{\infty}, which specifies the height and depth of the character so that the limits can be better placed (though this may depend on the fonts that the viewer has installed).

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    $\begingroup$ You might consider \mathop{\vcenter{\huge ⦿}}_{n=1}^{\infty} as more semantic and a little easier to use, plus it centers the operator, and \limits will work with that: $$\mathop{\vcenter{\huge ⦿}}_{n=1}^{\infty} abc$$ Even better might be \mathop{\vcenter{\huge\unicode[.67,.15]{x29BF}}}_{n=1}^{\infty}, which specifies the height and depth of the character so that the limits can be better placed (though this may depend on the fonts that the viewer has installed). $\endgroup$ Feb 10 at 18:07
  • $\begingroup$ @DavideCervone thank you $\vcenter{\stackrel{⦿{\tiny \triangle} ⦿}{\smile}}$ I have added this verbatim to the answer. $\endgroup$ Feb 11 at 12:59
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    $\begingroup$ Love the smile face! $\endgroup$ Feb 11 at 16:12

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