# What does $\mathbb{R}_{++}$ stand for? [closed]

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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## closed as unclear what you're asking by GEdgar, MJD, Giuseppe Negro, Harish Chandra Rajpoot, Silvia GhinassiFeb 1 at 0:32

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I don't think it is standard notation. Where have you seen it? – Henning Makholm Sep 2 '12 at 20:24
I would say: Look in the previous pages of that book. – GEdgar Sep 2 '12 at 21:01
Maybe it's a programming language... :-) – Asaf Karagila Sep 2 '12 at 21:46
Since HELP never came back, maybe we can close this. – GEdgar Jan 31 at 17:53

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 $(0,\infty)$. – cyberSingularity Sep 2 '12 at 21:43
I have seen it used this way fairly often. – Michael Greinecker Sep 2 '12 at 21:45
--in economics books. – Michael Greinecker Sep 2 '12 at 21:54

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.

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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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