function [ dXdt ] = KristenHorstmannDE(t,X)
% this function defines the differential equation
global V K 

dXdt = zeros(size(X));

s=X(1);
dsdt=-V*s/(K+s);
dpdt=V*s/(K+s);

dXdt(1)=dsdt;
dXdt(2)=dpdt;

end