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/*
* Copyright ©️ 2024 Mario Forzanini <mf@marioforzanini.com>
*
* This file is part of my exercises for LSN.
*
* My exercises for LSN are free software: you can redistribute them
* and/or modify them 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.
*
* My exercises for LSN are distributed in the hope that they 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 my exercises for LSN. If not, see
* <https://www.gnu.org/licenses/>.
*
*/
#include <errno.h>
#include <math.h>
#include <stdbool.h>
#include <stdio.h>
#include <string.h>
#include "random.h"
#include "std.h"
#define TOTAL 10000
#define NBLOCK 100
#define BLOCK_THROWS (TOTAL / NBLOCK)
#define NSTEPS 100
#define DISCRETE_NAME "DISCRETE"
#define CONTINUOUS_NAME "CONTINUOUS"
typedef struct Vector3 Vector3;
typedef struct Polar Polar;
struct Vector3 {
double x, y, z;
};
struct Polar {
double theta, phi;
};
enum direction {
DIRECTION_MX = 0, /* (-1, 0, 0) */
DIRECTION_MY, /* ( 0, -1, 0) */
DIRECTION_MZ, /* ( 0, 0, -1) */
DIRECTION_X, /* ( 1, 0, 0) */
DIRECTION_Y, /* ( 0, 1, 0) */
DIRECTION_Z, /* ( 0, 0, 1) */
};
enum method {
METHOD_UNKNOWN = 0,
METHOD_DISCRETE,
METHOD_CONTINUOUS,
};
static Vector3 unit_vectors[] = {
{ -1, 0, 0 },
{ 0, -1, 0 },
{ 0, 0, -1 },
{ 1, 0, 0 },
{ 0, 1, 0 },
{ 0, 0, 1 },
};
enum direction
random_direction(Random rnd[static 1])
{
double x = random_rannyu(rnd);
return (enum direction)(floor(x / 6.));
}
Polar
random_polar(Random rnd[static 1])
{
return (Polar) {
.phi = random_rannyu_range(rnd, 0, 2. * M_PI),
.theta = acos(1 - 2 * random_rannyu(rnd)),
};
}
void
usage(char *argv0)
{
fprintf(stderr, "USAGE: %s [" DISCRETE_NAME "|" CONTINUOUS_NAME "]\n",
argv0);
exit(1);
}
static double avgs[NSTEPS] = { 0 }, avgs2[NSTEPS] = { 0 };
int
main(int argc, char *argv[])
{
FILE *primes, *input;
Random rnd = { 0 };
enum method method = METHOD_UNKNOWN;
if (!(primes = fopen("Primes", "r"))) {
STD_ERROR("Error opening Primes: %s\n", strerror(errno));
return 1;
} else if (!(input = fopen("seed.in", "r"))) {
STD_ERROR("Error opening seed.in: %s\n", strerror(errno));
return 1;
}
if (!random_init(&rnd, primes, input)) {
return 1;
}
if (argc < 2) {
usage(argv[0]);
} else {
if (strcmp(argv[1], DISCRETE_NAME) == 0) {
method = METHOD_DISCRETE;
} else if (strcmp(argv[1], CONTINUOUS_NAME) == 0) {
method = METHOD_CONTINUOUS;
} else {
STD_ERROR("Unknown method: %s\n", argv[1]);
usage(argv[0]);
}
}
switch (method) {
case METHOD_DISCRETE: {
/* FIXME(mario): I did not understand this... */
for (int steps = 0; steps < NSTEPS; steps++) {
for (int block = 0; block < NBLOCK; block++) {
double rmean_square = 0.0;
Vector3 r = { 0 };
for (int curr_throw = 0;
curr_throw < BLOCK_THROWS;
curr_throw++) {
for (int step = 0; step < steps;
step++) {
Vector3 dr = unit_vectors
[random_direction(
&rnd)];
r.x += dr.x;
r.y += dr.y;
r.z += dr.z;
}
rmean_square += (r.x * r.x + r.y * r.y
+ r.z * r.z);
}
rmean_square /= (double)(BLOCK_THROWS);
avgs[steps] += rmean_square;
avgs2[steps] += (rmean_square * rmean_square);
}
avgs[steps] /= (double)(NBLOCK);
printf("%lf %lf\n", avgs[steps],
sqrt(avgs2[steps]
/ (double)(NBLOCK)-avgs[steps]
* avgs[steps]));
}
} break;
case METHOD_CONTINUOUS: {
STD_TODO("Implement continuous RW.\n");
} break;
default:
__builtin_unreachable();
}
random_save_seed(&rnd, "seed.out");
return 0;
}
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