%simulation of a discrete Gompertz
function x=gen_dg(pars,reps,simlen)
a = pars.a;
b = pars.b;
s2 = pars.s2;
x1 = pars.initx;
dt = 1;
x = -99*ones(reps,simlen);
x(:,1) = x1;
for i = 2:simlen,
    x(:,i) = x(:,i-1)*a + b...
        +randn(reps,1)*sqrt(s2);
end