c++11 random doubles using uniform_real_distribution

Question

So I am trying to get uniform random doubles using the following for my random number generation:

std::random_device rd;
std::mt19937_64 randEng(rd());
std::uniform_real_distribution<double> rg(std::numeric_limits<double>::min(), std::numeric_limits<double>::max());

and then of course calling rg(randEng)

However if I use the numeric limits of the double like this I am not getting a random sample that are from -DOUBLE to +DOUBLE. Instead I am getting numbers that are in the order of maginute e+306 or e+307 or e+308. Is there something I am doing wrong here that will not allow me to get the range that I am looking for?

If I put in something else like -10, 10 to the uniform distribution I do get valid numbers in that range. Is there something going on here for doubles that I am missing?

double min gives me `2.2250738585072014e-308`, is this what you expecting? or you want negative double max — Bryan Chen, Sep 22 '14 at 03:28
http://stackoverflow.com/questions/1153548/minimum-double-value-in-c-c — Bryan Chen, Sep 22 '14 at 03:53

score 1 · Accepted Answer · answered Sep 22 '14 at 07:37

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std::numeric_limits<double>::min()

is the double value with smallest absolute value. if you want the smallest negative (highest abs), you can use

-std::numeric_limits<double>::max()

Technically, there may also be

numeric_limits<double>::has_infinity
-numeric_limits<double>::infinity()

But that does not seem to be what you want

answered Sep 22 '14 at 07:37

b.buchhold

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Don't forget [`std::numeric_limits::lowest()`](http://en.cppreference.com/w/cpp/types/numeric_limits/lowest). – rubenvb Sep 22 '14 at 07:51

score 0 · Answer 2 · edited Sep 22 '14 at 07:30

0

I'm not sure I understand the problem; std::numeric_limited<double>::min() will return something like 2.2250738585072014e-308, which is a positive value. It's in scientific notation; the e-308 means you want to move the decimal place to the left about 308 times.

edited Sep 22 '14 at 07:30

user1095108

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answered Sep 22 '14 at 05:34

NeomerArcana

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c++11 random doubles using uniform_real_distribution

2 Answers2