%computes the same code twice the difference in times is due to
%preallocation

N=500;
x=[0:1/N:1];
f=@(y) log(abs(y));

tic
for i=1:N+1
    K(:,i)=f(x-x(i));
end
t1=toc

tic
for i=1:N+1
    K(:,i)=f(x-x(i));
end
t2=toc