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Symbol for Direct sum

asked 2020-08-04 10:05:47 +0200

Daniel Volinski gravatar image

Hi All,

What is the proper way to write in math the symbol for direct sum: https://en.wikipedia.org/wiki/Direct_sum

It's a big circle with a plus sign in it and functions as an operator.


Daniel Volinski

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answered 2020-08-04 10:13:06 +0200

gabix gravatar image

updated 2020-08-04 10:14:46 +0200

Depends on what you mean under proper way.

I’d use the plain Unicode character ⊕ (U+2295).

If you want to use the Math syntax, it’s oplus.

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answered 2020-08-04 10:21:47 +0200

ajlittoz gravatar image

updated 2020-08-04 10:22:13 +0200

If you just use direct sum as a binary operator, enter A oplus B oplus C.

In case you need a summation operator, you can't use oplus which has a reserved meaning, you must force U+2295 CIRCLED PLUS (type the hexadecimal code and immediately Alt+X). The formula becomes:

oper ⊕ from {i=0} to n A_i

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Just a comment: Alt + X to convert a code to a character does not work in Math. At least, not for me.

gabix gravatar imagegabix ( 2020-08-04 10:25:08 +0200 )edit

@gabix: What's your OS and LO version? Here, Fedora Linux 32 + LO I checked the example before posting. Alt+X seems to work in all components (Writer, Calc, Draw, Math; not tried in Impress nor Base, but it should also work).

ajlittoz gravatar imageajlittoz ( 2020-08-04 10:29:47 +0200 )edit on Windows 7 (works in Writer, though).

Re-checked with portable. It works there.

gabix gravatar imagegabix ( 2020-08-04 10:30:48 +0200 )edit

U+2295 shows italicized; oplus normal.

Works in LibreOffice (x86); OS: Windows 6.1. Math and Impress also included.

LeroyG gravatar imageLeroyG ( 2020-08-04 16:38:32 +0200 )edit

It is italicised because Math considers it a "variable". Either use double quotes "⊕" (but it will be formatted with Text font) or see the trick in my answer to 252386/how-to-add-missing-characters-in-libreoffice-math-formula for using a custom font (and bold, italics, …)

ajlittoz gravatar imageajlittoz ( 2020-08-04 17:20:22 +0200 )edit
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Asked: 2020-08-04 10:05:47 +0200

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Last updated: Aug 04 '20