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/er/er_B.c | 126 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 126 insertions(+)
 create mode 100644 src/er/er_B.c

(limited to 'src/er/er_B.c')

diff --git a/src/er/er_B.c b/src/er/er_B.c
new file mode 100644
index 0000000..84a0b4b
--- /dev/null
+++ b/src/er/er_B.c
@@ -0,0 +1,126 @@
+/**
+ *  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 samples a graph from the Erdos-Renyi random graph
+ *  model B, i.e., the ensemble of graphs with N nodes where each of
+ *  the possible N(N-1)/2 edges is created with probability equal to
+ *  p, and independently from all the other edges.
+ *
+ *
+ *  References: 
+ *
+ *  [1] Erdős, P. & Rényi, A. On Random Graphs I Publ. Math. Debrecen,
+ *      6, 290 (1959)
+ *
+ *  [2] Erdos, P. & Renyi, A. On the evolution of random graphs
+ *      Publ. Math. Inst. Hungary. Acad. Sci., 5, 17-61 (1960)
+ *
+ */
+
+
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <time.h>
+
+void usage(char *argv[]){
+  printf("********************************************************************\n"
+         "**                                                                **\n"
+         "**                        -*-    er_B    -*-                      **\n"
+         "**                                                                **\n"
+         "**  sample an Erdos-Renyi graph of N nodes and edge probability p **\n"
+         "**                                                                **\n"
+         "**                  the output is an I,J matrix:                  **\n"
+         "**                            I_1 J_1                             **\n"
+         "**                            I_2 J_2                             **\n"
+         "**                            I_3 J_3                             **\n"
+         "**                            ... ...                             **\n"
+         "**                            I_K J_K                             **\n"
+         "**                                                                **\n"
+         "**               (output is to stdout or to a file)               **\n"
+         "**                                                                **\n"
+         "**      If a filename is specified as fourth parameter then       **\n"
+         "**         the degree sequence is dumped out to that file         **\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> <p> [<filout>]\n\n" , argv[0]);
+}
+
+
+
+int main(int argc, char *argv[]){
+
+  unsigned int N, i, j;;
+  FILE *fileout;
+  double p, val;
+  char error_str [256];
+
+  if(argc < 3){
+    usage(argv);
+    exit(1);
+  }
+  
+  N = atoi(argv[1]);
+  p = atof(argv[2]);
+  
+  
+  if (argc >3){
+    fileout = fopen(argv[3], "w+");
+    if (!fileout){
+      sprintf(error_str, "Error opening file %s", argv[3]);
+      perror(error_str);
+      exit(2);
+    }
+  }
+  else{
+    fileout = stdout;
+  }
+  
+  srand(time(NULL));
+
+  /* Loop over all nodes...*/
+  for(i=0; i<N; i++){
+    /* Loop over the nodes with label larger than i...*/
+    for(j=i+1; j<N; j++){
+      val = rand() * 1.0 / RAND_MAX;
+      /* if the sample is smaller than p, create the edge */
+      if (val < p){
+        fprintf(fileout, "%d %d\n", i, j);
+      }
+    }
+  }
+  fclose(fileout);
+}
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