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I have often seen, that users of this forum use "$.$" (full-stop) as a multiplication sign, e.g. $4.5=20$

I have thought, that this notation is the american style. But a user of this forum told me that this is not the case. Therefore my question is, in which country or context is this kind of notation used ?

Remark: I´m only interested in notation for multiplication of numbers. I´m not interested in, e.g., the notation for multiplication of two vectors. I´m familiar with "$\cdot$" and "$\times$" for muliplication signs.

Thanks for any answer.

callculus42
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    I think there may be some places where it is common. However, American mathematicians really do use a centered dot for multiplication, in Latex it is \cdot. So, instead of $4.5$ I would write $4 \cdot 5$ It is possible (I do not know) that some people intend \cdot but are not sure what they are doing, and type in a full-stop – Will Jagy Aug 31 '15 at 17:57
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    $4\cdot 5$ is the best, but $4\bullet 5$ is better for short-sighted people. – Dietrich Burde Aug 31 '15 at 17:58
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    @DietrichBurde $4 \bigcirc 5$ – Will Jagy Aug 31 '15 at 17:59
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    @WillJagy $4{\huge{\bigcirc}}5$ – Git Gud Aug 31 '15 at 18:01
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    I think I've seldom seen this in books published after about 1930 or so. I've seen it in 19th-century books. – Michael Hardy Nov 23 '16 at 15:43

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I'm not aware of this being a common notation anywhere, especially since it can be confused with a decimal point. I think some people use it because they aren't aware that the \cdot macro exists.

Dominik
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    Remarkably, older literature such as e.g. Whittaker & Watson's (1902) Course in modern analysis uses a vertically centered dot for the decimal point. – ccorn Aug 31 '15 at 18:31
  • To say nothing of the Europeans who use a comma for the decimal point...! – Zhen Lin Aug 31 '15 at 19:02
  • @ZhenLin And for the thousand seperators the Europeans and maybe others use a point instead of a comma. – callculus42 Aug 31 '15 at 19:43