> On Monday 17 June 2002 20:46, you wrote:
> > Hello guys!
> >
> > Can someone explain me how to use the random and srandom
> > (or their half-equals rand() and srand(),) in linux ? because the
> > man page doesn't really help much, and my programming books
> > have nothing about it...
> >
> > Thanks in advance,
> > Eliran
> >From NUMERICAL RECIPES IN C: THE ART OF SCIENTIFIC COMPUTING (www.nr.com),
> chptr 7:
> "Now our first, and perhaps most important, lesson in this chapter is: be
> very, very suspicious of a system-supplied rand() that resembles the one just
> described. If all scientific papers whose results are in doubt because of bad
> rand()s were to disappear from library shelves, there would be a gap on each
> shelf about as big as your fist..."
> Read the whole chapter for more..
> (http://www.ulib.org/webRoot/Books/Numerical_Recipes/bookcpdf/c7-0.pdf though
> ../c7-8.pdf)
>
The reference you mentioned (Numerical_Recipes) already been referred
to:
Quoting rand (3):
NOTES
The versions of rand() and srand() in the Linux C Library
use the same random number generator as random() and sran
dom(), so the lower-order bits should be as random as the
higher-order bits. However, on older rand() implementa
tions, the lower-order bits are much less random than the
higher-order bits.
In Numerical Recipes in C: The Art of Scientific Computing
(William H. Press, Brian P. Flannery, Saul A. Teukolsky,
William T. Vetterling; New York: Cambridge University
Press, 1992 (2nd ed., p. 277)), the following comments are
made:
"If you want to generate a random integer between 1
and 10, you should always do it by using high-order
bits, as in
j=1+(int) (10.0*rand()/(RAND_MAX+1.0));
and never by anything resembling
j=1+(rand() % 10);
(which uses lower-order bits)."
Random-number generation is a complex topic. The Numeri_
cal Recipes in C book (see reference above) provides an
excellent discussion of practical random-number generation
issues in Chapter 7 (Random Numbers).
For a more theoretical discussion which also covers many
practical issues in depth, please see Chapter 3 (Random
Numbers) in Donald E. Knuth's The Art of Computer Program_
ming, volume 2 (Seminumerical Algorithms), 2nd ed.; Read
ing, Massachusetts: Addison-Wesley Publishing Company,
1981.
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