% bias
function re=v_std(ang,loop_out)
ang
len_mean=0;
for i=1:loop_out
    len_mean=len_mean+ang(i);
end
len_mean=len_mean/loop_out

re_std=0;
for i=1:loop_out
    re_std=re_std+(ang(i)-len_mean)*(ang(i)-len_mean)';
end
re=sqrt(re_std)/(loop_out-1);