Wikipedia lists several dot characters in Unicode. These are the ones that are ambiguous to me:

- interpunct, middle dot (·)
`·`

`·`

`U+00B7`

“midpoint (in typography)” - dot operator (⋅)
`⋅`

`⋅`

`U+22C5`

- bullet operator (∙)
`∙`

`U+2219`

“(mathematics)” - bullet (•)
`•`

`•`

`U+2022`

“black small circle” “often used to mark list items”

I’m mostly interested in the Unicode characters, but Math.SE told me to try here, and LaTeX likewise has:

`\cdot`

`\cdotp`

`\bullet`

`\textbullet`

For example:

- Wikipedia shows multiplication as both “x ⋅ y” (“dot operator”) and “x ∙ y” (“bullet operator”) in the same paragraph.
- WP List of mathematical symbols uses “middle dot” for multiplication.
- WP Multiplication article uses
`\cdot`

for scalar multiplication. - WP says the matrix dot product should be written using the “bullet operator” character, like “
**a**∙**b**“. - The WP Dot product article uses the LaTeX
`\cdot`

character for dot products. - Wikipedia shows a raised decimal point example “£21·48”, which uses the “middle dot” character.
- Wikipedia notates chemistry hydrates like “CuSO4 · 5H2O”, which uses the “middle dot” character.
- Combined units can also be written with a dot, like “N·m”. Wikipedia uses a “middle dot” for this, not the “dot operator”.
- Characters in SI notations has a paragraph on combined units, seeming to say that dot operator is preferred for this, like “N⋅m”.
- Wolfram Alpha considers
`\cdot`

and`·`

to be equivalent, as well as`\bullet`

and`•`

. Valid?

Of course it’s pedantic, they all look the same, and the meaning can always be assumed from context, but I’d like to know, once and for all, which Unicode/HTML and LaTeX characters are *semantically* correct in each application?

(If there are other examples I left out, feel free to edit the question and add them.)

The following is my personal view on this matter. I have not seen hard rules anywhere.

Normal mathematics

The \cdot is a multiplication symbol. The following are all equivalent

xy = x⋅y = x×y

It is useful in thermo-fluid dynamics formulas where there are a lot of multi character values such as Reynolds number, Prandtl number, etc.

s = Pr⋅Re⋅v

Compound SI units (see siunitx package) is also multiplication

1 N = 1 kg⋅m/s^2

For vector-tensors it is element wise multiplication

enter image description here

Chemical formula

I don’t know much about chemical notation (ask Joseph Wright)

Decimal marker

The center dot as decimal marker is only found in very old books or non-scientific literature. Because it can be confused with a multiplication sign is is not used in scientific literature any more.