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researchv10 Dan Cross

.TH RAND 3
.CT 2 math
.SH NAME
rand, lrand, frand, nrand, srand \(mi random number generator
.SH SYNOPSIS
.nf
.B int rand()
.PP
.B long lrand()
.PP
.B double frand()
.PP
.B int nrand(val)
.B int val;
.PP
.B srand(seed)
.B int seed;
.fi
.SH DESCRIPTION
.I Rand
uses a linear feedback
random number generator
to return uniform pseudo-random
numbers
.I x,
.if t .RI 0\(<= x <2\u\s715\s10\d,
.if n 0<=x<2^15,
with period about
.if t 2\u\s732\s0\d.
.if n 2^32.
.PP
.I Lrand
returns a uniform long
.I x,
.if t .RI 0\(<= x <2\u\s731\s10\d,
.if n 0<=x<2^31,
with period about
.if t 2\u\s748\s0\d.
.if n 2^48.
.PP
.I Frand
returns a uniform double
.I x,
.if t .RI 0.0\(<= x <1.0,
.if n 0.0<=x<1.0,
always a multiple of
.if t 2\u\s7\-31\s0\d.
.if n 2^-31.
.PP
.I Nrand
returns a uniform integer
.I x,
.if t .RI 0\(<= x < val.
.if n 0<=x<val.
.PP
The generators are initialized by calling
.I srand
with whatever you like as argument.
To get a different starting value each time,
.IP
.L
srand((int)time((long *)0));
.LP
will work as long as it is not called more often
than once per second.
.SH BUGS
.I Rand
and
.I lrand
are quite machine-dependent.
Although
.I frand
and
.I nrand
are more portable, they appear in few versions of Unix.

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