Solved

Random numbers

Posted on 1998-10-18
3
168 Views
Last Modified: 2010-03-05
I need a section of code to generate a random number between 0 and some value n and then round it down
0
Comment
Question by:jedimike
  • 2
3 Comments
 
LVL 5

Accepted Solution

by:
b2pi earned 20 total points
ID: 1205474
'round it down' is a bit confusing.

Basically, though, you first need to set a seed if your perl is before
v 5.004 (If you don't, you'll get random numbers, but everytime you
run  the program, you could get about the same random numbers).  Just
to be safe, then


srand( time ^ $$ );

(There are many quibbles that the above might not be random enough.
Chances are, it is. If not, go to www.perl.com and search for
TrulyRandom)

Having seeded, you get a random value r (0 <= r < y ) by calling

$r = rand(y);

if n is a relatively large integer, then, you could do

$r = int(rand(n))

0
 
LVL 84

Expert Comment

by:ozo
ID: 1205475
I would prefer ( time + $$ ) as a seed over ( time ^ $$ )
If $$ has a tendancy to be increasing, it could be easy for ( time ^ $$ ) to be tha same on subsequent runs.
(Using 5.004 may be even more preferred)
0
 
LVL 5

Expert Comment

by:b2pi
ID: 1205476
That requires that $$ is increasing at about the same rate as is time,
so $$ is approximately uniformly (approximately uniformly? Mea culpa,
mea maxima culpa) increasing by 1 per second.  If I remember my
combinatorics correctly (backed up by the perldoc page on srand) that
_still_ gives a 1 in 3 chance of being identical, nu? So if you're on
a machine that is averaging 1 pid per second (no more, no less), then
you've a 1 in 3 chance of problems.  If one's that worried about it,
best go to TrulyRandom, or, my all time favorite, make use of
http://lavarand.sgi.com 
0

Featured Post

DevOps Toolchain Recommendations

Read this Gartner Research Note and discover how your IT organization can automate and optimize DevOps processes using a toolchain architecture.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Suggested Solutions

On Microsoft Windows, if  when you click or type the name of a .pl file, you get an error "is not recognized as an internal or external command, operable program or batch file", then this means you do not have the .pl file extension associated with …
There are many situations when we need to display the data in sorted order. For example: Student details by name or by rank or by total marks etc. If you are working on data driven based projects then you will use sorting techniques very frequently.…
Explain concepts important to validation of email addresses with regular expressions. Applies to most languages/tools that uses regular expressions. Consider email address RFCs: Look at HTML5 form input element (with type=email) regex pattern: T…
This video shows how to use Hyena, from SystemTools Software, to bulk import 100 user accounts from an external text file. View in 1080p for best video quality.

778 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question