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Diffstat (limited to 'src/er/er_B.c')
| -rw-r--r-- | src/er/er_B.c | 126 |
1 files changed, 126 insertions, 0 deletions
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); +} |