In mathematics, we often see a symbol that looks like a capital R but made with double lines with space between them. What is this symbol called? Or is it just called
“the symbol for the real numbers”? And what is the whole history of how they came up with it instead of using something like RR for instance, which would be easier to type than this strange symbol?
signed, Resting on my Matrix Waiting for an Answer
You mean this?
¶
I have no idea.
Reeder, the symbol you show means “paragraph” and is commonly used by proofreaders to show that a new paragraph should start here. It’s even in the LATIN-1 character set.
Sorry, don’t know the story behind the other - I think I have seen it as an uppercase R with an additional vertical line just to the left of the regular one - right?
I believe that it’s pronounced “script R”. When mathematics was being deleoped, little concern was given to how it would be typed; after all, typing has been around for far less time than mathematics. Furthermore, something like “RR” would be confusing because it looks like two symbols, when it is meant to be one symbol. If you wish to represent the real numbers in a computer document, the standard way of doing so is by use of a bold R.
I am pretty sure that is the symbol for “all real numbers”.
I can’t answer the OP, but in the math classes I have taken, the symbol for the set of natural numbers is an N with double lines on the left side, and the symbol for the rationals is a Q with an extra vertical line inside, and on the left, of the Q. I guess there’s sort of a “double line” convention at work here.
The symbol is probably most often referred to as “the set of real numbers”. Originally, in mathematical typography, the symbol was simply a bold R. However, this posed a problem for mathematicians lecturing on a chalk board, as there’s no such thing as bold chalk. Thus someone started drawing letters with double lines and it caught on. Now the double-line letters are even used in typeset documents.
In LaTeX, the computer typesetting system which is the most popular among mathematicians, the symbol is produced with the macro \mathbb{R}. The “bb” stands for “blackboard”. So maybe you could call the symbol “blackboard R”, though I’ve never heard it referred to that way.
I just like words and figured there is probably a term for this doubled up R used for the real numbers. I learned some years ago that for & there is the name “ampersand.” And we used to call * an asterisk back in the old days, but now it is called star. # is called sharp in music and pound, I think, on telephones and in computer. Some books used to have an asterisk for the first footnote and a thing that looked like a religious cross for the second footnote andit was called a dagger.
For the third footnote there was another symbol that I can’t recall.
I just ran across this very topic at MathWorld:
“A letter of the alphabet drawn with doubled vertical strokes is called doublestruck, or sometimes blackboard bold (because doublestruck characters provide a means of indicating bold font weight when writing on a blackboard).”
What you have there is a doublestruck R.