From 3aee2fd43e3059a699af2b63c6f2395e5a55e515 Mon Sep 17 00:00:00 2001
From: KatolaZ <katolaz@freaknet.org>
Date: Wed, 27 Sep 2017 15:06:31 +0100
Subject: First commit on github -- NetBunch 1.0

---
 src/ws/ws.c | 204 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 204 insertions(+)
 create mode 100644 src/ws/ws.c

(limited to 'src/ws/ws.c')

diff --git a/src/ws/ws.c b/src/ws/ws.c
new file mode 100644
index 0000000..bfbe102
--- /dev/null
+++ b/src/ws/ws.c
@@ -0,0 +1,204 @@
+/**
+ *  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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