randGen.randomize(seed);
q[centre][centre] = 1;
double r1 = 3.0;
double r2 = 3.0 * r1;
for (int i = 0; i < _max_iter; i++) {
double phi = pi2 * randGen.random();
double ri = r1 * Math.cos(phi);
double rj = r1 * Math.sin(phi);
int ci = centre + (int) (ri + 0.5);
int cj = centre + (int) (rj + 0.5);
short qt = 0;