rand() v. rand(0.1) ?

[7stud --]

Is there any difference between calling rand() and rand(0.1)?

 

[Florian Frank]

Is there any difference between calling rand() and rand(0.1)?

------------------------------------------------------------ Kernel#rand
rand(max=0) => number

 

[Chad Perrin]

------------------------------------------------------------ Kernel#rand
rand(max=0) => number

Speaking of which . . . obviously rand() doesn't produce a truly random
number, but it's reasonably close for some purposes. I'm curious about
just how far off it is, though -- because I'm curious about how
appropriate it is to use to simulate dice-rolling for gaming software (in
the "roleplaying game" sense of the term "gaming") in Ruby's
implementation. I'd prefer some kind of a general feel for it before I
write software to statistically analyze the output of millions of
iterations of rand() evaluations.

 

[Matthew Rudy]

Is there any difference between calling rand() and rand(0.1)?

takes a look at the rdoc -
http://www.ruby-doc.org/core/classes/Kernel.html#M005955

its defined as "rand(max=0)"
ie. calling rand() is exactly the same as rand(0)

also it "Converts max to an integer using max1 = max.to_i.abs"
ie. max = 0.1 -> max1 = 0.1.to_i.abs = 0
ie. rand() results in the same behaviour as rand(0.1)

 

[Chad Perrin]

Hi,

In message "Re: rand() v. rand(0.1) ?"

|Speaking of which . . . obviously rand() doesn't produce a truly random
|number, but it's reasonably close for some purposes. I'm curious about
|just how far off it is, though -- because I'm curious about how
|appropriate it is to use to simulate dice-rolling for gaming software (in
|the "roleplaying game" sense of the term "gaming") in Ruby's
|implementation.

It uses Mersenne Twister algorithm which has a period of 2**19937-1.

Excellent! Thank you for the quick and informative response.

 

[7stud --]

takes a look at the rdoc -
http://www.ruby-doc.org/core/classes/Kernel.html#M005955

its defined as "rand(max=0)"
ie. calling rand() is exactly the same as rand(0)

also it "Converts max to an integer using max1 = max.to_i.abs"
ie. max = 0.1 -> max1 = 0.1.to_i.abs = 0
ie. rand() results in the same behaviour as rand(0.1)

That was my analysis too, however pickaxe2 has some code on p. 138 that
calls rand(0.1).

 

[Morton Goldberg]

That was my analysis too, however pickaxe2 has some code on p. 138
that
calls rand(0.1).

You've found a bug in the Pickaxe book. I'm guessing but I suspect that

sleep(rand(0.1))

should be

sleep(0.1 * rand)

That is, I think the idea was to sleep in the range 0.0 to 0.1
seconds, not 0.0 to 1.0 seconds.

Regards, Morton