float fitness() {
    // calcular las distancias
    float dist = 0;
    for ( unsigned i = 0; i < FILESIZE; i ++ ) {
	float dist1 = (__sample[i][0] - __gen[0]);
	float dist2 = (__sample[i][1] - __gen[1]);
	dist += sqrt( dist1*dist1 + dist2*dist2);
    }
    return 1/dist;
}