{ diff(x1, t) = (1*k19*k1*x1*(1 - x1/k2) + (-1)*k19*k3*x1*x2 + (-1)*k19*k9*x1*x3/(k11 + x3))/k19,
  diff(x2, t) = (1*k19*k5 + (-1)*k19*k6*x2 + 1*k19*k7*x1*x2/(k8 + x1) + (-1)*k19*k4*x1*x2 + (-1)*k19*k10*x2*x3/(k12 + x3) + 1*k19*k14)/k19,
  diff(x3, t) = ((-1)*k19*k13*x3 + 1*k19*piecewise(k17/(1/8), t <= 1/8, piecewise(k17/(1/8), and(t >= 21, t <= 21 + 1/8), piecewise(k17/(1/8), and(t >= 42, t <= 42 + 1/8), piecewise(k17/(1/8), and(t >= 63, t <= 63 + 1/8), piecewise(k17/(1/8), and(t >= 84, t <= 84 + 1/8), piecewise(k17/(1/8), and(t >= 105, t <= 105 + 1/8), piecewise(k17/(1/8), and(t >= 126, t <= 126 + 1/8), 0))))))))/k19 }