function y = fd( x )
%drift function 
    y=zeros(2,1);
%     y(1)=-x(2);
%     y(2)=x(1);
%circular
%     
%     y(1)=x(2);
%     y(2)=(1-x(1)^2)*x(2)-x(1);
%van der Pol

%       y(1)=1;
%       y(2)=x(2)*(2-x(2));
%       if (x(2)<0) y(2)=0;
 %feller logistic
 
%   y(1)=1; 
%   y(2)=-x(2)/(1-x(1));
 %Brownian bridge
 
%     mu=0.1;
%     y(1)=1;
%     y(2)=mu*x(2);
   %Black-Scholes-Merton
   
%    y(1)=1;
%    y(2)=0;
   %stoch. exp.
   
     y(1)=1;
    y(2)=x(2)-x(2)^3; y(2)=x(2)-3*sin(x(2)); %y(2)=x(2)-x(2)^2;
   %bistable
 
    
end



