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I come from Norway, and here the formatting of maths are a little bit different than in the U.S. and the UK. If you want to factorize 25, you know that it is 5 times 5. How would you write this with LaTeX? In Norway we would write 5⋅5, and as far as I've seen, with LaTeX, you would write: $5\times 5$ ( 5 x 5 )

Is there a difference, or is one of them wrong? Which one actually means times?

Werner
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Friend of Kim
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    Use $5\cdot 5$. – azetina May 15 '12 at 18:35
  • It depends on the context and the tradition. BTW: If you are native from Norway, you might be able to read my Danish LaTeX book, just googl my name and latexbog – daleif May 15 '12 at 18:37
  • Yepp, I can. I'll do :) Danish and Norwegian is written almost the same, as you know. :) Great to have a LaTeX course in my "almost native" language! – Friend of Kim May 15 '12 at 18:39
  • @daleif But, I'm using it only for my website, and to process maths with a PHP-script. I don't use LaTeX as a language. – Friend of Kim May 15 '12 at 18:40
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    I'm not convinced that this is a Norwegian speciality! Using a dot for multiplication is quite common in mathematics beyond school-level. – Andrew Stacey May 15 '12 at 18:52
  • @AndrewStacey Ok. But why do I see the \times so often over at math.stackexchange.com? – Friend of Kim May 15 '12 at 18:55
  • @AndrewStacey: According to the omnipotent Wikipedia "The middle dot is standard in the United States, the United Kingdom, and other countries where the period is used as a decimal point. In other countries that use a comma as a decimal point, either the period or a middle dot is used for multiplication." (http://en.wikipedia.org/wiki/Multiplication#Notation_and_terminology) – Jake May 15 '12 at 19:07
  • Yes, we do use a comma instead of a period to indicate decimals. – Friend of Kim May 15 '12 at 19:30
  • @50ndr33 No idea. Maybe because lots of the people there have school-level maths so people use \times to ensure there's no misunderstanding. – Andrew Stacey May 15 '12 at 19:36
  • @AndrewStacey Hvilken bruker du, personlig, da? – Friend of Kim May 15 '12 at 19:39
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    @50ndr33 Det avhenger. Personlig, bruker jeg det meste ingen ting, slik x y. Jeg bruker \cdot kun hvis det er nødvendig å klare noe, f.eks 2 \cdot 3, eller jeg vil skire at studentene skjønner at jeg menner å multipliserer de tingene. (Beklager at norsken min er litt dårlig) – Andrew Stacey May 15 '12 at 19:51
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    In Spain \times is used by children at school. \cdot is used by mathemacians, scientifics and engineers. \cdot has two advantages: · it's shorter and cleaner and it can't be confused with the ex letter. – skan Oct 18 '15 at 10:22
  • I am well-versed in math, and the following is fairly global. Children tend to use the "x", which in latex is \times. Older folks use a dot, which in latex is \cdot. There is an actual distinction in math, where the dot means "scalar product" and the "x" means "matrix multiplication". To "regular folks", the scalar product is the "normal" multiplication they think of. – Mike Williamson Sep 20 '18 at 04:03

4 Answers4

33

you can use $5\cdot 5$ to create the way used in Norway. I don't know the mathematical difference as I'm not that firm in mathematics ;-) But this is a way to just create the output you want.

Stephan Lukasczyk
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    Personally I use the \times symbol only in three different occasions: (1) the cross product –vector product– (e.g., \vec j \times \vec k = \vec{\imath}); (2) to write dimensions (e.g., $3 \times 3$ matrix); (3) to write numbers in scientific notation –to visually know if the whole expression is a number or a multiplication– (e.g., 2.5 \times 10^3 \cdot 3 \times 10^2 is a multiplication of two “scientific” numbers). For everything else I use the usual · (\cdot). – Manuel Mar 29 '13 at 17:32
6

It both means the same, multiplication. The used symbol depends on your location. If you want to have a centred dot, you can use \cdot instead.

Marco
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  • But, if they're all correct, and means multiplication: Why is the dot called cdot, instead of something more like multiplication like times is? – Friend of Kim May 15 '12 at 18:38
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    cdot means centered dot. With regards to the choice of calling name, well that is left to how the initial writer decided it to be. – azetina May 15 '12 at 18:40
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    @50ndr33: There are other dots as well, like . (a period), \ddot as an accent (and \dddot and \ddddot, provided by amsmath, I think). – Werner May 15 '12 at 18:41
  • And \dot is for Newton-style differentiation. For example, \( \dot x \). – Mike Renfro May 15 '12 at 18:54
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    @Marco -- if i remember rightly from a basic mechanics course, many years ago, a "dot product" is a scalar product (like $5 \cdot 5$), and a "cross product" is a vector product (my memory isn't good enough to come up with a decent example). this level of distinction isn't recognized until after secondary school. – barbara beeton May 15 '12 at 20:12
5

I agree with the rest of the answers, that \cdot is the way to have multiplication represented by a dot, as seem to be usual in many countries. However, I would suggest that when dealing with a notation that is language, country or region specific, you define your own command. In this case you can for example do \let\times\cdot in the preamble of your document.

That way, if your document ever gets translated to another language, the translator does not have to go and change all the math equations and formulas, they just need to replace your \let command by, for example, \let\times\longrightarrow if they are translating to a language in which multiplication is denoted by a long right arrow.

Jan Hlavacek
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3

amsmath package defines a \dots command, which is similar to the existing \ldots command. In Math, the \cdot command can be used to represent the centered dot multiplication symbol as opposed to the conventional \times symbol and similar to \ldots we have \cdots.

Hence to get the centered dot in your example, you need to input:

$5\cdot 5$

azetina
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