{ diff(x1, t) = (1*k7*k1*x1*(1 - x1/k2) + (-1)*k7*21/200000*exp((-t)/(1681/10))*x1*x2)/k7,
  diff(x2, t) = 1*k7*k4*x2*(1 - x2/(k5 + k6*x1*x2))/k7 }