Surely it must be possible to initialize rand with current date and
time.
Documents seem to indicate this is done with rand(0) or srand with no
value. I
have tried both methods and I get the same tired old sequence of
numbers. I
would write my own random number generator except I don’t know how to
get a
numeric value out of Time.
Charles G.
I haven’t played with rand, but
Time.now.to_i
should get you a useful seed value.
-jroOn 11/28/06, [email protected] [email protected] wrote:
Surely it must be possible to initialize rand with current date and time.
Documents seem to indicate this is done with rand(0) or srand with no value. I
have tried both methods and I get the same tired old sequence of numbers. I
would write my own random number generator except I don’t know how to get a
numeric value out of Time.
Can you post the code that isn’t working for you?
http://www.rubycentral.com/ref/ref_m_kernel.html#rand
http://www.rubycentral.com/ref/ref_m_kernel.html#srand
ruby -e ‘print “#{rand}\t#{rand}\t#{rand}\n”’
0.346093491828657 0.0992270243895501 0.491676115802907
ruby -e ‘print “#{rand}\t#{rand}\t#{rand}\n”’
0.11466702118189 0.0119319523512537 0.111031191235015
ruby -e ‘print “#{rand}\t#{rand}\t#{rand}\n”’
0.282694845926778 0.570101702949362 0.303077309354919
ruby -e ‘srand(1); print “#{rand}\t#{rand}\t#{rand}\n”’
0.417022004702574 0.720324493442158 0.000114374817344887
ruby -e ‘srand(1); print “#{rand}\t#{rand}\t#{rand}\n”’
0.417022004702574 0.720324493442158 0.000114374817344887
ruby -e ‘srand(1); print “#{rand}\t#{rand}\t#{rand}\n”’
0.417022004702574 0.720324493442158 0.000114374817344887
ruby -e ‘srand(2); print “#{rand}\t#{rand}\t#{rand}\n”’
0.435994902142004 0.0259262318278913 0.549662477878709
ruby -e ‘srand(2); print “#{rand}\t#{rand}\t#{rand}\n”’
0.435994902142004 0.0259262318278913 0.549662477878709
ruby -e ‘srand(2); print “#{rand}\t#{rand}\t#{rand}\n”’
0.435994902142004 0.0259262318278913 0.549662477878709
ruby -v
ruby 1.8.4 (2005-12-24) [i586-linux]
On 11/28/06, [email protected] [email protected] wrote:
Surely it must be possible to initialize rand with current date and
time. Documents seem to indicate this is done with rand(0) or srand
with no value. I have tried both methods and I get the same tired old
sequence of numbers. I would write my own random number generator
except I don’t know how to get a numeric value out of Time.
I’m not sure which documents you’re reading. These are the ri docs I
see (examples elided for brevity):
Converts _max_ to an integer using max1 = max+.to_i.abs+. If the
result is zero, returns a pseudorandom floating point number
greater than or equal to 0.0 and less than 1.0. Otherwise, returns
a pseudorandom integer greater than or equal to zero and less than
max1. +Kernel::srand+ may be used to ensure repeatable sequences of
random numbers between different runs of the program. Ruby
currently uses a modified Mersenne Twister with a period of
219937-1.
Seeds the pseudorandom number generator to the value of
_number_.+to_i.abs+. If _number_ is omitted or zero, seeds the
generator using a combination of the time, the process id, and a
sequence number. (This is also the behavior if +Kernel::rand+ is
called without previously calling +srand+, but without the
sequence.) By setting the seed to a known value, scripts can be
made deterministic during testing. The previous seed value is
returned. Also see +Kernel::rand+.
So no, providing an argument to Kernel#rand does not set the seed, it
provides the range. Kernel#srand is used for setting the seed value.
As you indicated, calling Kernel#srand with no argument should reset
the seed to a value based on the current time (+ process id and
sequence number).
However, you should not even need to call Kernel#srand to set the seed
to the current time unless you’ve already reseeded to something else
first. When the Ruby interpreter starts up Kernel#srand is
(effectively) called with no argument to initialize the RNG.
This can be seen with the following test program:
$ cat rand_test.rb
puts rand
puts rand
puts rand
$ ruby rand_test.rb
0.386885926082005
0.0444309071556157
0.147546420511617
$ ruby rand_test.rb
0.882099491922559
0.984145785659405
0.590537113434846
As you can see, each run of the program got a different set of random
numbers without ever needing to call srand.
To answer you last question, if you ever do need an integer
representing the current time, you can use +Time.now.to_f.to_i+.
Time.now gives you the current time as an object, Time#to_f converts
it to the number of milliseconds since the epoch and then Float#to_i
to truncate it down to an integer. You can also do +Time.now.to_i+ but
that’s grained to the second instead of milliseconds.
Jacob F.
On Nov 28, 2006, at 12:51 PM, [email protected] wrote:
Surely it must be possible to initialize rand with current date and
time.
Documents seem to indicate this is done with rand(0) or srand with
no value. I
have tried both methods and I get the same tired old sequence of
numbers. I
would write my own random number generator except I don’t know how
to get a
numeric value out of Time.
Can’t reproduce your problem. #srand with no argument seems to seed
the pseudo-random number generator with a different value on each
call. For example:
srand
p Array.new(10) { rand(10) }
srand(1)
p Array.new(10) { rand(10) }
srand
p Array.new(10) { rand(10) }
srand(1)
p Array.new(10) { rand(10) }
srand
p Array.new(10) { rand(10) }
[7, 8, 8, 1, 8, 3, 5, 6, 5, 2]
[4, 9, 7, 9, 0, 1, 3, 9, 1, 2]
[8, 4, 0, 0, 0, 7, 7, 4, 4, 4]
[4, 9, 7, 9, 0, 1, 3, 9, 1, 2]
[3, 9, 2, 9, 8, 0, 1, 0, 5, 9
Can you show us the code that didn’t work?
Regards, Morton
P.S. Concerning getting a numeric value out of Time:
Time.now.to_i
why not seed it from /dev/random/ in C/++ you’d do something like this:
unsigned int seed
FILE *devrandom = fopen("/dev/random", “r”);
fread(&seed,sizeof(seed),1,devrandom);
then pass the seed to rand, using the time itself is a bit dubious if
you want a strong set of random numbers, not a good idea for statistical
research / cryptography i fear.
On Nov 28, 2006, at 1011 , Christopher Coleman-Smith wrote:
why not seed it from /dev/random/
rand() is seeded by /dev/urandom by default.
–
Eric H. - [email protected] - http://blog.segment7.net
This implementation is HODEL-HASH-9600 compliant
On Nov 28, 2006, at 0951 , [email protected] wrote:
Surely it must be possible to initialize rand with current date and
time.
Documents seem to indicate this is done with rand(0) or srand with
no value. I
have tried both methods and I get the same tired old sequence of
numbers. I
would write my own random number generator except I don’t know how
to get a
numeric value out of Time.
On windows I think there is no way to seed from /dev/urandom, so you
get seeded by some default value. Instead the seed is composed of
the current time in seconds and microseconds and the pid.
–
Eric H. - [email protected] - http://blog.segment7.net
This implementation is HODEL-HASH-9600 compliant
This forum is not affiliated to the Ruby language, Ruby on Rails framework, nor any Ruby applications discussed here.
Sponsor our Newsletter | Privacy Policy | Terms of Service | Remote Ruby Jobs