function [ dXdt ] = posFeed( t, x )

% positive feedback loop dynamics 

% degradation of X 
dx = 0.5;

% degradation of Y 
dy = 0.5;

% Dyamics for LacI mRNA
dXdt(1,:) = 2*x(1)^2/(1+x(1)^2) - dx*x(1);

% Dyamics for LacI protein 
dXdt(2,:) = 2*x(1)^2/(4+x(1)^2) - dy*x(2);

end