function [v,sd] = ball(n,N)
M=20;
a=[];
for k=1:M % M independent runs
x=2*rand(n,N)-1; % random vectors in W_n
nq = sum(x.^2 , 1); % list of the 2-norms (squared) of the vectors
K = sum(nq<1); % number of vectors with norm <=1
a = [a,K/N]; % percentage of points in B_n
end
a_m = mean(a); % mean value of a
a_sd = std(a); % standard deviation of a
v = a_m * 2^n; % mean value of v
sd = a_sd * 2^n; % standard deviation of a