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What does $\mathbb{R}_{++}$ mean?

I know $\mathbb{R}_+$ means all non-negative real numbers, but I have no clue what $\mathbb{R}_{++}$ means.

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    I don't think it is standard notation. Where have you seen it?2012-09-02
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    I would say: Look in the previous pages of that book.2012-09-02
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    Maybe it's a programming language... :-)2012-09-02
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    Since HELP never came back, maybe we can close this.2016-01-31

3 Answers 3

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It usually means the set of all positive real numbers, $\mathbb{R}_{++} = (0,\infty)$. Of course, there might be more symbols for this set.

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    Right, because $\mathbb{R}_{+}$ is ambiguous, as some authors use it for $[0,\infty)$ and some for $(0,\infty)$.2012-09-02
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    I have seen it used this way fairly often.2012-09-02
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    --in economics books.2012-09-02
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    But don't most math books use $\mathbb{R}^{+}$ instead?2017-04-29
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From my Course: Probabilistic Methods in Finance, we denoted $R+, R++$ like so: $$R+ =\{x\in R : x\ge0\}$$ $$R++ =\{x\in R : x≫0\}.$$

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    What does $ x≫0 $ mean? Shouldn't it be $\mathbb{R}_{++} =\{x\in \mathbb{R} : x>0\}$.2017-08-14
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Im not completely sure , but i believe it means strictly positive. Thus not the negative reals NOR zero.

Well assuming the context is real numbers that is.

I believe it is used in countries where R+ is meant to include 0. In most countries R+ does not include 0 , hence the extra symbol.

It might help to read over again to get an idea.