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