NAME
lcrans - linear congruential pseudo-random number generators
SYNOPSIS
cc [ flag ... ] file ... -lsunmath -lm [ library ... ]
#include <sunmath.h>
int i_lcran_(void);
float r_lcran_(void);
double d_lcran_(void);
void i_lcrans_(int *x, int *n, int *l, int *u);
void u_lcrans_(unsigned *x, int *n, unsigned *l, unsigned
*u);
void r_lcrans_(float *x, int *n, float *l, float *u);
void d_lcrans_(double *x, int *n, double *l, double *u);
void i_get_lcrans_(int *x);
void i_set_lcrans_(int *x);
void i_init_lcrans_(void);
DESCRIPTION
These functions generate uniformly distributed random
numbers of types int, unsigned int, float, or double. They
share a common internal generator that produces a sequence
of integers between 1 and LCRAN_MODULUS - 1 using the
recurrence
next = (multiplier * last) % LCRAN_MODULUS
LCRAN_MODULUS is defined in <sunmath.h> and has the value
2**32 - 1. The multiplier depends on which function is
called as described below.
i_lcran_() returns a random integer between 1 and
LCRAN_MODULUS - 1 = 2**32 - 2. It always uses the value
16807 as a multiplier.
r_lcran_() returns a random single precision floating point
number between 1 / LCRAN_MODULUS and 1. It always uses the
value 16807 as a multiplier.
d_lcran_() returns a random double precision floating point
number between 1 / LCRAN_MODULUS and 1 - (1 /
LCRAN_MODULUS). It always uses the value 16807 as a multi-
plier.
i_lcrans_(n, x, l, u), u_lcrans_(n, x, l, u), r_lcrans_(n,
x, l, u), and d_lcrans_(n, x, l, u) each fill the array ele-
ments x[0], ..., x[*n-1] with random 32-bit signed integers,
32-bit unsigned integers, single precision floating point
numbers and double precision floating point numbers, respec-
tively. The numbers are scaled and offset so as to be uni-
formly distributed over the interval [*l, *u]. These func-
tions use the multiplier supplied in the most recent call to
i_set_lcrans_; the default multiplier, which is also reset
by i_init_lcrans_, is 16807.
i_get_lcrans_(x) sets x[0] to the last value produced by the
internal generator and x[1] to the current multiplier used
by i_lcrans_, u_lcrans_, r_lcrans_, and d_lcrans_.
i_set_lcrans_(x) sets the value used by the internal genera-
tor to compute the next random number (i.e., the value of
last in the recurrence above) to x[0] and the mulitplier
used by i_lcrans_, u_lcrans_, r_lcrans_, and d_lcrans_ to
x[1]. The value of last should be between 1 and
LCRAN_MODULUS - 1. Only the least significant 22 bits of
the multiplier are used.
i_init_lcrans_() resets the value of last to 1 and the mul-
tiplier to 16807.
All of the functions listed above use the same internal gen-
erator. Consequently, calling i_lcran_ immediately after
calling i_init_lcrans_ will give a different result than
calling i_init_lcrans_, then u_lcrans_, then i_lcran_. Dif-
ferent threads within a program use different generators,
however, so calling one of these functions in one thread
will not affect the values delivered when the same function
is called from another thread.
EXAMPLES
To generate 1000 random double precision numbers in [0,1):
double x[1000];
int i;
for (i = 0; i < 1000; i++)
x[i] = d_lcran_();
The same numbers can be generated more efficiently using:
double x[1000], lb, ub;
int n = 1000;
lb = D_LCRAN_LB; /* defined in <sunmath.h> */
ub = D_LCRAN_UB; /* defined in <sunmath.h> */
d_lcrans_(x, &n, &lb, &ub);
To generate 1000 random integers between -10 and 10:
int x[1000], n = 1000, lb = -10, ub = 10;
i_lcrans_(x, &n, &lb, &ub);
SEE ALSO
addrans(3M), drand48(3C), mwcrans(3M), rand(3C), random(3C),
shufrans(3M).
Knuth, Seminumerical Algorithms, 1981, Addison-Wesley.
Park and Miller, Random Number Generators: Good Ones are
Hard to Find, Communications of the ACM, October 1988.
NOTES
Typically, the addrans(3M) generators are faster than either
the lcrans(3M) or the mwcrans(3M) generators.