Understanding formula for generating random number in interval

Asked Jan 08 '16 at 07:31

Active Jan 08 '16 at 07:36

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I know that there are plenty of posts on this topic, but I can't find any that explain clearly enough for me why the formula works the way it does.

On Mozilla's page to get a random number in (min, max), we have

function getRandomIntInclusive(min, max) {
    return Math.floor(Math.random() * (max - min + 1)) + min;
}

But I don't understand how that is. If I take [4,10] for example,

r * (10 - 4) -> [0,6) // r to represent a random number in [0,1)
r * (10 - 4 + 1) -> [0, 7)
(r * (10 - 4 + 1)) + 4 -> [4, 11)

I don't know how that's supposed to give a random number in [4,10]. Could someone please explain?

Also, how do I get a random number in the open interval (a, b)?

asked Jan 08 '16 at 07:31

TheRealFakeNews

2

Have you referred this: http://stackoverflow.com/questions/1527803/generating-random-numbers-in-javascript-in-a-specific-range – Rayon Jan 08 '16 at 07:33
Since we are dealing with integers, `[4,10]` is the same as `[4, 11)`. To generate anteger in `(a,b)` simply note that this is the same as `[a+1, b-1]`. – Klas Lindbäck Jan 08 '16 at 11:04
@KlasLindbäck But how do I generate a real number (not an integer) in (a, b)? – TheRealFakeNews Jan 08 '16 at 17:31
@RayonDabre Yes, I did. I read the chosen solution over and over. I understand it now by Klas's comment. However, the post doesn't say how to generate a real number in (a,b). – TheRealFakeNews Jan 08 '16 at 17:32
@AlanH Surely you mean floating point? – Klas Lindbäck Jan 11 '16 at 08:09

0 Answers0