m=25000;
t0=clock;
g=rand(1,m);
for s=1:m
p(s)=-log(g(s));
end
m1=mean(p);

s1=std(p)^2;t1=clock;
durata1=etime(clock,t0);
tt=1:1:100;p1=5.*p;
hist(p1,tt)
durata2=etime(clock,t1);