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/* Copyright (c) 2019, Anthony Latorre <tlatorre at uchicago>
*
* This program is free software: you can redistribute it and/or modify it
* under the terms of the GNU General Public License as published by the Free
* Software Foundation, either version 3 of the License, or (at your option)
* any later version.
* This program is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
* more details.
* You should have received a copy of the GNU General Public License along with
* this program. If not, see <https://www.gnu.org/licenses/>.
*/
#include "random.h"
#include <math.h>
#include <gsl/gsl_rng.h>
#include <gsl/gsl_randist.h>
static gsl_rng *r;
double randn(void)
{
/* Generates a random number from a normal distribution using the
* Box-Muller transform. */
double u1, u2;
u1 = genrand_real1();
u2 = genrand_real1();
return sqrt(-2*log(u1))*cos(2*M_PI*u2);
}
void rand_sphere(double *dir)
{
/* Generates a random point on the unit sphere. */
double u, v, theta, phi;
u = genrand_real1();
v = genrand_real1();
phi = 2*M_PI*u;
theta = acos(2*v-1);
dir[0] = sin(theta)*cos(phi);
dir[1] = sin(theta)*sin(phi);
dir[2] = cos(theta);
}
/* Randomly choose `k` elements from array `src` with `n` elements with
* probabilities proportional to `w`. The elements are sampled without
* replacement and placed into the `dest` array. */
void ran_choose_weighted(int *dest, double *w, size_t k, int *src, size_t n)
{
int i, j;
gsl_ran_discrete_t *g;
size_t index, result;
int duplicate;
if (!r)
r = gsl_rng_alloc(gsl_rng_default);
g = gsl_ran_discrete_preproc(n, w);
i = 0;
while (i < k) {
index = gsl_ran_discrete(r, g);
result = src[index];
duplicate = 0;
for (j = 0; j < i; j++) {
if (result == dest[j]) {
duplicate = 1;
break;
}
}
if (!duplicate) dest[i++] = result;
}
gsl_ran_discrete_free(g);
}
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