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 Gray
I haven't played with rand, but
Time.now.to_i
should get you a useful seed value.
-jro
On Nov 28, 2006, at 11:51 AM, Smgspices@aol.com 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.Charles Gray
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, Smgspices@aol.com <Smgspices@aol.com> wrote:
I'm not sure which documents you're reading. These are the ri docs I
see (examples elided for brevity):
------------------------------------------------------------ Kernel#rand
rand(max=0) => number
On 11/28/06, Smgspices@aol.com <Smgspices@aol.com> 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.
------------------------------------------------------------------------
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.
----------------------------------------------------------- Kernel#srand
srand(number=0) => old_seed
------------------------------------------------------------------------
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
$ 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 Fugal
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.
Smgspices@aol.com 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.
Charles Gray
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:
<code>
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) }
</code>
<results>
[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
</results>
Can you show us the code that didn't work?
Regards, Morton
P.S. Concerning getting a numeric value out of Time:
<code>
Time.now.to_i
</code>
On Nov 28, 2006, at 12:51 PM, Smgspices@aol.com 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.
On Nov 28, 2006, at 0951 , Smgspices@aol.com 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.
--
Eric Hodel - drbrain@segment7.net - http://blog.segment7.net
This implementation is HODEL-HASH-9600 compliant
rand() is seeded by /dev/urandom by default.
On Nov 28, 2006, at 1011 , Christopher Coleman-Smith wrote:
why not seed it from /dev/random/
--
Eric Hodel - drbrain@segment7.net - http://blog.segment7.net
This implementation is HODEL-HASH-9600 compliant