Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!cs.utexas.edu!usc!apple!oliveb!tymix!tardis!jms
From: jms@tardis.Tymnet.COM (Joe Smith)
Newsgroups: comp.sys.amiga
Subject: Re: Lattice random number functions
Keywords: Lattice, Random numbers
Message-ID: <769@tardis.Tymnet.COM>
Date: 9 Nov 89 07:58:43 GMT
References: <755@dsacg2.UUCP>
Reply-To: jms@tardis.Tymnet.COM (Joe Smith)
Organization: McDonnell Douglas Field Service Co, San Jose CA
Lines: 31

In article <755@dsacg2.UUCP> nor1675@dsacg2.UUCP (Michael Figg) writes:
>I have very little experience with random number generators but have a need now.
>I tried the Lattice function 'drand48' last night, but it always returns 0.

If you don't change the seed, pseudo-random number generators produce a fixed
pattern of numbers each time you start the program.  This is very handy when
trying to debug your program.  While it is true that drand48() returns
0.0000 on the first call, the succeeding calls produce other numbers.

After the program is working the way you want it, you can add a call to
srand or srand48 at the top of the program.  Make sure srand is called only
once (not in a loop), and give it a a fairly random number, such as the
time of day of when the program started.

#include <math.h>
#include <time.h>
void main() {
  double x;
  int i;
/* comment out the next line to get a consistent sequence of numbers */
  srand48(time(0L));		/* set seed to current time */
  for ( i=0; i<10; i++) {
    x = drand48();
    printf("%f\n",x);
  }
}
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Joe Smith (408)922-6220 | SMTP: JMS@F74.TYMNET.COM or jms@gemini.tymnet.com
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