{ diff(x1, t) = ((-1)*(k1*x7*x1 + k2*x11*x1 + k3*x5*x1) + 1*k10*x6*x2)/k33,
  diff(x2, t) = (1*(k1*x7*x1 + k2*x11*x1 + k3*x5*x1) + (-1)*k10*x6*x2 + 1*k8 + (-1)*k9*x2 + 1*k19*x2)/k33,
  diff(x3, t) = (1*(k1*x7*x1 + k2*x11*x1 + k3*x5*x1) + (-1)*k32*x3)/k33,
  diff(x4, t) = ((-1)*k4*x5*x4 + 1*k5*x5 + 1*(k6*x2 + k7) + (-1)*k11*x4)/k33,
  diff(x5, t) = (1*k4*x5*x4 + (-1)*k5*x5 + (-1)*k16*x5*x8 + 1*k17*x9 + (-1)*k22*x5*x5)/k33,
  diff(x6, t) = ((-1)*k10*x6*x2 + 1*k28/(1 + k29*x10) + 1*k30 + (-1)*k31*x6 + 1*k32*x3)/k33,
  diff(x7, t) = (1*k12 + (-1)*k13*x7 + (-1)*k18*x7*x10 + (-1)*k20*x8*x7 + 1*k21*x11)/k33,
  diff(x8, t) = (1*k14 + (-1)*k15*x8*x5 + (-1)*k16*x5*x8 + 1*k17*x9 + (-1)*k20*x8*x7 + 1*k21*x11 + (-1)*k23*x8)/k33,
  diff(x9, t) = (1*k16*x5*x8 + (-1)*k17*x9)/k33,
  diff(x10, t) = ((-1)*k18*x7*x10 + 1*k24 + (-1)*k25*x10 + 1*k26/(1 + k27*x6))/k33,
  diff(x11, t) = (1*k20*x8*x7 + (-1)*k21*x11)/k33 }