function yt=nonsys(y,t,ylower,yupper,mod,a,b)


am=a(mod);
bm=b(mod);
cov=0.1;
%yt=exp(-am*y(t-1)^bm+sqrt(cov)*randn);
%yt=sin(2*pi*t/21);
yt=sin(5*pi*y(t-1))+1;

if yt<ylower
  yt=ylower;
elseif yt>yupper
  yt=yupper;
end