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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 simple graph (i.e., without self-loops
* and/or multiple edges) from the configuration model, using the
* degree sequence provided as input.
*
*/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include "utils.h"
#include "iltree_double.h"
#define MAXREJECTS 1000000
/* Usage */
void usage(char *argv[]){
printf("********************************************************************\n"
"** **\n"
"** -*- conf_model_deg -*- **\n"
"** **\n"
"** Sample a simple graph from the configuration model associated **\n"
"** to the degree sequence provided as input. **\n"
"** **\n"
"** The degree sequence is a file with format: **\n"
"** **\n"
"** k_1 **\n"
"** k_2 **\n"
"** k_3 **\n"
"** .... **\n"
"** k_N **\n"
"** **\n"
"** where 'k_i' is the degree of the i-th node. The program **\n"
"** prints on output the edge-list of the resulting graph. **\n"
"** **\n"
"** The second (optional) parameter 'threshold' indicates the **\n"
"** number of edge stubs that are allowed to remain unmatched **\n"
"** in the final graph. This parameter might be used to **\n"
"** obtain a graph from a too-constrained degree sequence, e.g., **\n"
"** a power-law sequence whose maximum degree is larger than **\n"
"** the structural cut-off. **\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"
" Please visit http://www.complex-networks.net for more information\n\n"
" (c) Vincenzo Nicosia 2010-2017 (v.nicosia@qmul.ac.uk)\n"
"********************************************************************\n\n"
);
printf("Usage: %s <degs> [<threshold>]\n\n" , argv[0]);
}
unsigned int count_stubs(unsigned int *nodes, int N){
int i;
unsigned int cnt;
cnt = 0;
for (i=0; i<N; i ++){
cnt += nodes[i];
}
return cnt;
}
void sample_graph_conf(unsigned int *nodes, int N, iltree_t *t,
unsigned int thresh){
unsigned int S;
unsigned int i, j;
unsigned int n_stubs;
unsigned int *stubs;
unsigned int countreject;
unsigned int L1, L2, I1, I2, tmp;
long double k;
FILE *tmp_file;
n_stubs = count_stubs(nodes, N);
if (n_stubs %2){
fprintf(stderr, "The sequence is not even!\n");
exit(3);
}
/* ind = malloc(n_stubs * sizeof(unsigned int)); */
/* stub2node = malloc(n_stubs * sizeof(unsigned int)); */
stubs = malloc(n_stubs * sizeof(unsigned int));
do{
countreject = 0;
S = 0;
/*
* We first initialize the stubs
*
* This is needed only before the first iteration, indeed....
*
*/
for(i=0; i<N; i ++){
for(j=0; j<nodes[i]; j ++){
stubs[S] = i;
S += 1;
}
}
while (S > 0 && countreject < MAXREJECTS){
/* sample the first stub */
L1 = rand() % S;
I1 = stubs[L1];
S -= 1;
/* sample the second stub */
L2 = rand() % S;
I2 = stubs[L2];
S -= 1;
if (L1 == L2){/* If L1 and L2 are the same element, discard the
sample */
/* reset S to the value it had before */
S += 2;
continue;
}
if (I1 == I2){
/* reject the pair: it's the same node! */
countreject += 1;
/* reset S to the value it had before */
S += 2;
continue;
}
if (I1 > I2){ /* we require that I1 < I2 */
tmp = I2;
I2 = I1;
I1 = tmp;
}
k = 1.0 * (I2)* (I2-1) / 2 + I1 + 1; /* This number represents the
couple I1, I2 (I1 < I2)*/
if (!iltree_lookup(*t, &k)){ /* The element "k" is not yet present in the BST*/
/* We can accept the new pair... */
/* ...so we insert it into the tree */
iltree_insert(*t, &k);
/* remove the two stubs */
tmp = stubs[L1];
stubs[L1] = stubs[S+1];
stubs[S+1] = tmp;
tmp = stubs[L2];
stubs[L2] = stubs[S];
stubs[S] = tmp;
}
else{/* reject the pair */
/* reset S to the value it had before */
countreject += 1;
S += 2;
}
}
/* Let's check if we got a graph....*/
if (countreject >= MAXREJECTS){
if (S <= thresh){
fprintf(stderr, "Found a graph (unmatched stubs: %d <= threshold: %d)\n",
S, thresh);
break;
}
else{
fprintf(stderr, "Graph not found (unmatched stubs: %d > threshold: %d)\n",
S, thresh);
S = 0;
countreject = 0;
tmp_file = iltree_get_fileout(*t);
iltree_destroy(*t);
*t = NULL;
*t = iltree_double_init(*t, tmp_file);
}
}
else{
fprintf(stderr, "Found a graph!\n");
break;
}
} while(1);
free(stubs);
}
int main(int argc, char *argv[]){
unsigned int *nodes= NULL;
int N;
iltree_t t = NULL;
FILE *filein;
unsigned int thresh;
if (argc < 2){
usage(argv);
exit(1);
}
srand(time(NULL));
if (!strcmp(argv[1], "-")){
/* take the input from STDIN */
filein = stdin;
}
else {
filein = openfile_or_exit(argv[1], "r", 2);
}
if (argc > 2) /* Set the threshold */
thresh = atoi(argv[2]);
else
thresh = 0;
t = iltree_double_init(t, stdout);
N = read_deg_seq(filein, &nodes);
sample_graph_conf(nodes, N, &t, thresh);
iltree_double_dump_edges(t);
fclose(filein);
free(nodes);
iltree_destroy(t);
}
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