function sig = sig_3(z)
[n1,n2] = size(z);
sig = zeros(n1,n2);
star = floor(n1/2);
sig(1:star) = 1+5*exp(1*ones(star,n2)./z(1:star));
sig(star+1:n1) = 1+5*exp(1*ones(n1-star,n2)./z(star+1:n1));