double integrand_n3z(int izdash, int iz) {
		int counter;
		double zdash, res, eps;

		eps = 0.25 * mesh_sc * Dia;

		counter = iz + izdash;
		zdash = izdash * mesh_sc * Dia;

		if ((counter < start) || (counter > (size - 1 - start)))
			res = 0.;
		else if ((iz == 0) && (izdash == start))
			res = eps * (Dia + eps) * eps * rho_sc.get(start + 1)
					/ (mesh_sc * Dia);
		else if ((iz == size - 1) && (izdash == -start))
			res = eps * (Dia + eps) * eps * rho_sc.get(start + 1)
					/ (mesh_sc * Dia);
		else
			res = (rho_sc.get(counter)) * (0.25 * Dia * Dia - zdash * zdash);

		if (Math.abs(res) < 1E-10)
			res = 0.;
		return res;
	}