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Summary

Description
English: Examples of A) Degree centrality, B) Closeness centrality, C) Betweenness centrality, D) Eigenvector centrality, E) Katz centrality and F) Alpha centrality.
Date
Source Own work
Author Claudio Rocchini

Licensing

I, the copyright holder of this work, hereby publish it under the following license:
w:en:Creative Commons
attribution share alike
This file is licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license.
You are free:
  • to share – to copy, distribute and transmit the work
  • to remix – to adapt the work
Under the following conditions:
  • attribution – You must give appropriate credit, provide a link to the license, and indicate if changes were made. You may do so in any reasonable manner, but not in any way that suggests the licensor endorses you or your use.
  • share alike – If you remix, transform, or build upon the material, you must distribute your contributions under the same or compatible license as the original.

Source Code

The source code needs http://www.gnu.org/s/gsl/ . 

/**********************************
 * (C)2012 Claudio Rocchini       *
 *  www.rockini.name              *
 *  CC-BY 3.0                     *
 **********************************/
 
#include <stdio.h>
#include <stdlib.h>
#include <vector>
#include <gsl/gsl_matrix.h>
#include <gsl/gsl_linalg.h>
#include <gsl/gsl_eigen.h>
#include "rand.h"

static inline unsigned char f2b( double f ) {
	if(f<0) f = 0; if(f>1) f = 1;
	int i = int(f*256);
	return i<0 ? 0 : i>255 ? 255 : i;
}
 
void HSV2RGB(double h, double s, double v, unsigned char rgb[3] ) {
	if (s == 0) {
		rgb[0] = rgb[1] = rgb[2] = f2b(v);
	} else {
		double v_h = h * 6;
		double v_i = floor(v_h);
		double v_1 = v * (1 - s);
		double v_2 = v * (1 - s * (v_h - v_i));
		double v_3 = v * (1 - s * (1 - (v_h - v_i)));
		double v_r,v_g,v_b;
		if (v_i == 0) {v_r = v;   v_g = v_3; v_b = v_1;}
		else if (v_i == 1) {v_r = v_2; v_g = v;   v_b = v_1;}
		else if (v_i == 2) {v_r = v_1; v_g = v;   v_b = v_3;}
		else if (v_i == 3) {v_r = v_1; v_g = v_2; v_b = v  ;}
		else if (v_i == 4) {v_r = v_3; v_g = v_1; v_b = v  ;}
		else               {v_r = v;   v_g = v_1; v_b = v_2;};

		rgb[0] = f2b(v_r);
		rgb[1] = f2b(v_g);
		rgb[2] = f2b(v_b);
	}
}

class point2 {
public:
	double x,y;
};

double squared_dist( const point2 & p, const point2 & q ) {
	const double dx = p.x - q.x;
	const double dy = p.y - q.y;
	return dx*dx+dy*dy;
}

class edge {
public:
	int a,b;
	edge() {}
	edge( int na, int nb ): a(na),b(nb) {}
};

void floyd_warshall( int NV, const std::vector<edge> & e,
					 std::vector<double> & dist, std::vector<int> & conn ) {
	dist.resize(NV*NV); conn.resize(NV*NV);
	std::fill(dist.begin(),dist.end(),0.0);
	std::fill(conn.begin(),conn.end(),-1);
	std::vector<edge>::const_iterator ie;
	for(ie=e.begin();ie!=e.end();++ie) {
		dist[(*ie).a+NV*(*ie).b] = 1;
		dist[(*ie).b+NV*(*ie).a] = 1;
	}
	for(int k=0;k<NV;++k) for(int i=0;i<NV;++i) for(int j=0;j<NV;++j)
	if((dist[i+NV*k] * dist[k+NV*j] != 0) && (i != j))
		if((dist[i+NV*k] + dist[k+NV*j] < dist[i+NV*j]) || (dist[i+NV*j] == 0)) {
			conn[i+NV*j] = k;
			dist[i+NV*j] = dist[i+NV*k] + dist[k+NV*j];
		}
}

void central_degree( int NV, const std::vector<edge> & e, std::vector<double> & C ) {
	std::fill(C.begin(),C.end(),0.0);
	std::vector<edge>::const_iterator i;
	for(i=e.begin();i!=e.end();++i) {
		C[(*i).a] += 1;
		C[(*i).b] += 1;
	}
}

void central_closeness( int NV, const std::vector<edge> & e, std::vector<double> & C ) {
	std::vector<double> dist;
	std::vector<int> conn;
	floyd_warshall(NV,e,dist,conn);
	for(int i=0;i<NV;++i) {
		C[i] = 0;
		for(int j=0;j<NV;++j) C[i] += dist[i+NV*j];
		if(C[i]!=0.0) C[i] = 1.0/C[i];
	}
}

void central_betweenness( int NV, const std::vector<edge> & e, std::vector<double> & C ) {
	std::vector<double> dist; std::vector<int> conn;
	floyd_warshall(NV,e,dist,conn);
	std::fill(C.begin(),C.end(),0.0);
	for(size_t i=0;i<conn.size();++i)
		if(conn[i]>=0 && conn[i]<NV) C[conn[i]] += 1.0;
	for(size_t j=0;j<C.size();++j) C[j] = log(1+C[j]); // NOTE: the log!
}

void central_eigenvector( int NV, const std::vector<edge> & e, std::vector<double> & C ) {
	int i,j;
	gsl_eigen_symmv_workspace * w = gsl_eigen_symmv_alloc(NV);
	gsl_matrix * A    = gsl_matrix_alloc(NV,NV);
	gsl_vector * eval = gsl_vector_alloc(NV);
	gsl_matrix * evec = gsl_matrix_alloc(NV,NV);
	for(i=0;i<NV;++i) for(j=0;j<NV;++j)
		gsl_matrix_set(A,i,j,0.0); 
	for(std::vector<edge>::const_iterator ei=e.begin();ei!=e.end();++ei) {
		gsl_matrix_set(A,(*ei).a,(*ei).b,1.0);
		gsl_matrix_set(A,(*ei).b,(*ei).a,1.0);
	}
	gsl_eigen_symmv(A,eval,evec,w);
	int maxj = 0; double maxv = gsl_vector_get(eval,0);
	for(j=1;j<NV;++j)
		if(maxv<gsl_vector_get(eval,j)) {
			maxv = gsl_vector_get(eval,j);
			maxj = j;
		}
	for(i=0;i<NV;++i)
		C[i] = log(gsl_matrix_get(evec,i,maxj));	// NOTE: the log!
	gsl_matrix_free(evec);
	gsl_vector_free(eval);
	gsl_matrix_free(A);
	gsl_eigen_symmv_free(w);
}

void central_katz( int NV, const std::vector<edge> & e, std::vector<double> & C ) {
	const double alpha = 0.5;
	std::vector<double> dist; std::vector<int> conn;
	floyd_warshall(NV,e,dist,conn);
	for(int i=0;i<NV;++i) {
		C[i] = 0.0;
		for(int j=0;j<NV;++j) if(i!=j)
			C[i] += pow(alpha,dist[i+NV*j]);
	}
}

void central_alpha( int NV, const std::vector<edge> & e, std::vector<double> & C ) {
	const double alpha = 0.1;
	int i,j;
	gsl_matrix * A    = gsl_matrix_alloc(NV,NV);
	for(i=0;i<NV;++i) for(j=0;j<NV;++j)
		gsl_matrix_set(A,i,j,0.0); 
	for(std::vector<edge>::const_iterator ei=e.begin();ei!=e.end();++ei) {
		gsl_matrix_set(A,(*ei).a,(*ei).b,1.0);
		gsl_matrix_set(A,(*ei).b,(*ei).a,1.0);
	}
	for(i=0;i<NV;++i) for(j=0;j<NV;++j) {
		double t = -alpha*gsl_matrix_get(A,i,j);
		if(i==j) t += 1.0;
		gsl_matrix_set(A,i,j,t);
	}
	gsl_vector * x = gsl_vector_alloc(NV);
	gsl_vector * b = gsl_vector_alloc(NV);
	for(i=0;i<NV;++i) gsl_vector_set(b,i,1.0);
	gsl_linalg_HH_solve(A,b,x);
	for(i=0;i<NV;++i) C[i] = gsl_vector_get(x,i);
	gsl_vector_free(b);
	gsl_vector_free(x);
	gsl_matrix_free(A);
}

void central( int NV, const std::vector<edge> & e, std::vector<double> & C, double & minv, double & maxv, int m )  {
	C.resize(NV);
	switch(m) {
	case 0: central_degree(NV,e,C); break;
	case 1: central_closeness(NV,e,C); break;
	case 2: central_betweenness(NV,e,C); break;
	case 3: central_eigenvector(NV,e,C); break;
	case 4: central_katz(NV,e,C); break;
	case 5: central_alpha(NV,e,C); break;
	}
	minv = maxv = C[0];
	for(int i=1;i<NV;++i) {
		if(minv>C[i]) minv = C[i];
		if(maxv<C[i]) maxv = C[i];
	}
}

int main() {
	const int N = 256;
	const int NR = 3;
	const int NC = 2;
	const double SS = 300;
	const double SX=SS*NC, SY=SS*NR;
	const double R=5, B=6;
	const double MD2=(0.03)*(0.03),D2=(0.1)*(0.1);
	int i,j;
	point2 pts[N];

	for(i=0;i<N;++i)
		do {
			pts[i].x = DRand();
			pts[i].y = DRand();
			for(j=0;j<i;++j) if(squared_dist(pts[i],pts[j])<MD2) break;
		} while(j<i);

	std::vector<edge> edges;
	for(i=0;i<N-1;++i) for(j=i+1;j<N;++j)
		if(squared_dist(pts[i],pts[j])<D2) 
			edges.push_back(edge(i,j));
	
	FILE * fo = fopen("central.svg","w");
	fprintf(fo,
		"<?xml version=\"1.0\" encoding=\"UTF-8\" standalone=\"no\"?>\n"
		"<svg xmlns:svg=\"http://www.w3.org/2000/svg\" xmlns=\"http://www.w3.org/2000/svg\"\n"
		"version=\"1.0\" width=\"%g\" height=\"%g\" id=\"central\">\n"
		,SX,SY
	);
	
	for(int ir=0;ir<NR;++ir) {
		for(int ic=0;ic<NC;++ic) {
			std::vector<double> C;
			double minv,maxv;
			central(N,edges,C,minv,maxv,ic+NC*ir);
	 
			fprintf(fo,"<g style=\"stroke:#000000;stroke-width:1;stroke-linejoin:round;fill:none\">\n");
			for(i=0;i<int(edges.size());++i)
				fprintf(fo,"<line x1=\"%6.2f\" y1=\"%6.2f\" x2=\"%6.2f\" y2=\"%6.2f\"/>\n"
					,SX*ic/NC + (SX/NC-B*2)*pts[edges[i].a].x
					,SY*ir/NR + (SY/NR-B*2)*pts[edges[i].a].y
					,SX*ic/NC + (SX/NC-B*2)*pts[edges[i].b].x
					,SY*ir/NR + (SY/NR-B*2)*pts[edges[i].b].y
				);
			fprintf(fo,"</g>\n");
			for(i=0;i<N;++i) {
				unsigned char rgb[3];
				HSV2RGB( (2*(maxv-C[i]))/(3*(maxv-minv)),0.9,1.0,rgb);
				fprintf(fo,"<circle cx=\"%6.2f\" cy=\"%6.2f\" r=\"%6.2f\" style=\"stroke:#000000;"
				           "stroke-width:0.5;stroke-linejoin:round;fill:#%02X%02X%02X\"/>\n"
					,SX*ic/NC + (SX/NC-B*2)*pts[i].x
					,SY*ir/NR + (SY/NR-B*2)*pts[i].y
					,R
					,rgb[0],rgb[1],rgb[2]
				);
			}
		}
	}
	fprintf(fo,"</svg>\n");
	fclose(fo);
	return 0;
}

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Date/TimeThumbnailDimensionsUserComment
current15:01, 15 November 2012Thumbnail for version as of 15:01, 15 November 2012600 × 900 (476 KB)RocchiniUser created page with UploadWizard

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