#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<math.h>
#include<time.h>
#define Nrunmax 1
#define T 1000
#define kappa 1.

//This program produces the adjacency matrices of the Bianconi-Barabasi model 
//displaying the BEC condensation for different values of beta using the format read by cytoscape

int *k;//k[i] degree of  node i 
float Norm, *eta;//Norm normalization constant, eta[i] fitness of node i


int Choose(int it){
	// This subroutine choose the node j to which the node it is joined (m=1) 
	int j,i2;
	float x;
	
	x=Norm*drand48(); // draw a random number between 0 and Norm
	for(i2=0;i2<it;i2++){
		x-=eta[i2]*k[i2];
		if(x<0){
			j=i2;
			break;
		}
	}//finds the corresponding value of j
	
	
}

int main(int argc, char** argv){
	int i,j,it;
	float beta;// inverse temperature of the model
	char filec[60];
	FILE *fp;
  

  

	srand48(time(NULL));
	for (beta=0.3;beta<20.; beta=beta*2){ //loop on beta
		
		sprintf(filec,"BEC_adj_%2.3f.sif",beta);
		fp=fopen(filec,"w");
			
		/* Initialization of the vector k and eta */
		k=calloc(T,sizeof(int));
		eta=calloc(T,sizeof(float));
		for(i=0;i<T;i++){
			eta[i]=exp(-beta*pow(drand48(),1./(kappa+1.)));
		}
		/*Initial condition: one link connecting node 0 and node 1*/
		k[0]=1;
		k[1]=1;
		fprintf(fp, "%d xx %d\n", 1, 2);
		Norm=eta[1]+eta[0];
		
		for(it=2;it<T;it++){//The network grows, at each time the node it is added to the network with
		//m=1 link
			j=Choose(it);//The target node is chosen
			/*Updating of the degrees of the nodes and the Normalization constant*/
			k[j]++;
			k[it]++;
			Norm+=eta[j]+eta[it];
			/*Node it is connected to node j*/
			fprintf(fp, "%d xx %d\n", it+1, j+1);
		}
		fclose(fp);
	
		free (k);
		free(eta);
	}
	return 0;	
}