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/**
* 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
* <http://www.gnu.org/licenses/>.
*
* (c) Vincenzo Nicosia 2009-2017 -- <v.nicosia@qmul.ac.uk>
*
* This file is part of NetBunch, a package for complex network
* analysis and modelling. For more information please visit:
*
* http://www.complex-networks.net/
*
* If you use this software, please add a reference to
*
* V. Latora, V. Nicosia, G. Russo
* "Complex Networks: Principles, Methods and Applications"
* Cambridge University Press (2017)
* ISBN: 9781107103184
*
***********************************************************************
*
* This program creates a network using the Watts-Strogatz
* small-world network model.
*
* References:
*
* D. J. Watts and S. H. Strogatz. "Collective dynamics of
* 'small-world' networks". Nature 393 (1998), 440–442.
*
*
*/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include "utils.h"
void usage(char *argv[]){
printf("********************************************************************\n"
"** **\n"
"** -*- ws -*- **\n"
"** **\n"
"** Create a graph with 'N' nodes, using the Watts-Strogatz **\n"
"** small-world network model. The algorithm starts from a **\n"
"** circle graph with 'N' nodes and m*N edges, i.e. by putting **\n"
"** the 'N' nodes around a circle, so that each node is **\n"
"** connected to the 'm' closest nodes in the circle on each **\n"
"** direction. Then, each edge is rewired at random with **\n"
"** probability equal to 'p'. **\n"
"** **\n"
"** The output is an edge list in the format: **\n"
"** **\n"
"** I_1 J_1 **\n"
"** I_2 J_2 **\n"
"** I_3 J_3 **\n"
"** ... ... **\n"
"** I_K J_K **\n"
"** **\n"
"** If 'SHOW' is specified as a fourth parameter, the program **\n"
"** prints on STDERR the number of edges that were actually **\n"
"** rewired. **\n"
"** **\n"
"********************************************************************\n"
" This is Free Software - You can use and distribute it under \n"
" the terms of the GNU General Public License, version 3 or later\n\n"
" (c) Vincenzo Nicosia 2010-2017 (v.nicosia@qmul.ac.uk)\n\n"
"********************************************************************\n\n"
);
printf("Usage: %s <N> <m> <p> [SHOW]\n\n" , argv[0]);
}
/**
*
* This function checks if j is a neighbour of i, looking into the
* m positions of J starting at i*m
*
* In practice, the assumption is that J contains the m neighbours of
* node 0 in the first m positions, then the m neighbours of node 1,
* and to forth
*
*/
int __ws_is_neigh(unsigned int i, unsigned int j, unsigned int *J, unsigned int m){
int k;
for(k = i*m; k< (i+1)*m; k++){
if (J[k] == j)
return 1;
}
return 0;
}
int create_circle(unsigned int N, unsigned int m, unsigned int **J){
int K;
int i, j, l;
K = N *m;
*J = malloc(K * sizeof(unsigned int));
K = 0;
for(i=0; i<N; i++){
for(j=0; j < m; j++){
l = (i + j + 1) % N;
(*J)[K] = l;
K += 1;
}
}
return K;
}
int ws(unsigned int *J, unsigned int N, unsigned int m, double p){
unsigned int i, j, l, l1, num_rewire;
double xi;
num_rewire = 0;
for(i=0; i<N; i++){
for(j=0; j<m; j++){
l = (i+j) % N;
xi = 1.0 * rand() / RAND_MAX;
if (xi < p){
l1 = (int)(rand() % N);
if( (l1 != i) &&
(l1 != l) &&
!(__ws_is_neigh(i, l1, J, m))){
/* replace (i,l) with (i,l1) */
J[m * i + j] = l1;
num_rewire += 1;
}
else{
/* do nothing */
}
}
}
}
return num_rewire;
}
void dump_edges(unsigned int *J, unsigned int N, unsigned int m){
int i, j;
for(i=0; i<N; i++){
for(j=0; j<m; j++){
printf("%d %d\n", i, J[(m*i)+j]);
}
}
}
int main(int argc, char *argv[]){
int N, m, num_rewire;
unsigned int *J;
double p;
if(argc < 4){
usage(argv);
exit(1);
}
J = NULL;
N = atoi(argv[1]);
m = atoi(argv[2]);
p = atof(argv[3]);
create_circle(N, m, &J);
srand(time(NULL));
num_rewire = ws(J, N, m, p);
if (argc > 4 && !my_strcasecmp("SHOW", argv[4])){
fprintf(stderr, "Rewired edges: %d\n", num_rewire);
}
dump_edges(J, N, m);
free(J);
}
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