{ diff(x1, t) = (1*k21*k1*piecewise(0, and(t >= 0, t < 5), piecewise(1, and(t >= 5, t < 10), 0))/(k3 + piecewise(0, and(t >= 0, t < 5), piecewise(1, and(t >= 5, t < 10), 0))) + (-1)*k21*k4*x1)/k21,
  diff(x2, t) = (1*k21*k5*piecewise(1, and(t >= 0, t < 5), 0)/(k7 + piecewise(1, and(t >= 0, t < 5), 0)) + (-1)*k21*k8*x2)/k21,
  diff(x3, t) = (1*k21*k14*x1 + 1*k21*k15*x2 + (-1)*k21*k16*x3)/k21,
  diff(x4, t) = (1*k21*k17*x7 + 1*k21*k18*x3 + (-1)*k21*k19*x4)/k21,
  diff(x5, t) = (1*k21*k11*x2*x7 + (-1)*k21*k20*x5)/k21,
  diff(x7, t) = (1*k21*k10*(k13 - x7 - x5)*x1 + 1*k21*k9*(k13 - x7 - x5)*x4 + (-1)*k21*k12*x7 + (-1)*k21*k11*x2*x7)/k21 }