{ diff(x1, t) = (1*k3*x7 + (-1)*k25*x1 + (-1)*k23*x1)/k39,
  diff(x2, t) = (1*k32*x7 + (-1)*k35*x2 + (-1)*k34*x2)/k39,
  diff(x3, t) = (1*(k6 + k7*(x9 + x10))*x8 + (-1)*k26*x3 + (-1)*k24*x3)/k39,
  diff(x4, t) = (1*k23*x1 + (-1)*k25*x4 + (-1)*k23*x4)/k39,
  diff(x5, t) = (1*k34*x2 + (-1)*k35*x5 + (-1)*k34*x5)/k39,
  diff(x6, t) = (1*k24*x3 + (-1)*k26*x6 + (-1)*k24*x6)/k39,
  diff(x7, t) = (1*(k1*x12^k29/((1 + (x9 + x10)/k8)*(x12^k29 + k9^k29)) + k2*x11^k30/((1 + (x9 + x10)/k10)*(x11^k30 + k11^k30))) + (-1)*k18*x7/(x7 + k12))/k40,
  diff(x8, t) = (1*(k4 + k5*x12^k31/(x12^k31 + k13^k31)) + (-1)*k20*x8/(x8 + k14))/k40,
  diff(x9, t) = (1*k23*x4 + (-1)*k19*x9)/k40,
  diff(x10, t) = (1*k34*x5 + (-1)*k33*x10)/k40,
  diff(x11, t) = (1*k24*x6 + (-1)*k21*x11/(x11 + k15) + (-1)*(k27*k36*x11*(1 + tanh(24*(t - 24*floor(t/24) - k37)))*(1 - tanh(24*(t - 24*floor(t/24) - k38)))/4 - k28*x12))/k40,
  diff(x12, t) = (1*(k27*k36*x11*(1 + tanh(24*(t - 24*floor(t/24) - k37)))*(1 - tanh(24*(t - 24*floor(t/24) - k38)))/4 - k28*x12) + (-1)*k22*x12/(x12 + k16))/k40 }