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lammps/src/random_park.cpp
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random_park.cpp
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/* ----------------------------------------------------------------------
LAMMPS - Large-scale Atomic/Molecular Massively Parallel Simulator
www.cs.sandia.gov/~sjplimp/lammps.html
Steve Plimpton, sjplimp@sandia.gov, Sandia National Laboratories
Copyright (2003) Sandia Corporation. Under the terms of Contract
DE-AC04-94AL85000 with Sandia Corporation, the U.S. Government retains
certain rights in this software. This software is distributed under
the GNU General Public License.
See the README file in the top-level LAMMPS directory.
------------------------------------------------------------------------- */
// Park/Miller RNG
#include "math.h"
#include "random_park.h"
#define IA 16807
#define IM 2147483647
#define AM (1.0/IM)
#define IQ 127773
#define IR 2836
/* ---------------------------------------------------------------------- */
RanPark::RanPark(int seed_init)
{
seed = seed_init;
save = 0;
}
/* ----------------------------------------------------------------------
uniform RN
------------------------------------------------------------------------- */
double RanPark::uniform()
{
int k = seed/IQ;
seed = IA*(seed-k*IQ) - IR*k;
if (seed < 0) seed += IM;
double ans = AM*seed;
return ans;
}
/* ----------------------------------------------------------------------
gaussian RN
------------------------------------------------------------------------- */
double RanPark::gaussian()
{
double first,v1,v2,rsq,fac;
if (!save) {
int again = 1;
while (again) {
v1 = 2.0*uniform()-1.0;
v2 = 2.0*uniform()-1.0;
rsq = v1*v1 + v2*v2;
if (rsq < 1.0 && rsq != 0.0) again = 0;
}
fac = sqrt(-2.0*log(rsq)/rsq);
second = v1*fac;
first = v2*fac;
save = 1;
} else {
first = second;
save = 0;
}
return first;
}
/* ----------------------------------------------------------------------
reset the seed to a fractional (0-1) value of the total IM
------------------------------------------------------------------------- */
void RanPark::reset(double fraction)
{
seed = static_cast<int> (fraction*IM) + 1;
if (seed >= IM) seed = IM-1;
}
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