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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 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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