{ diff(x1, t) = (1*k66*ceiling(sin(pi*t/k65 + 1/1000)/2)*k1*x13 + 1*k66*k2*x9^k3/(k4^k3 + x9^k3) + (-1)*k66*k5*x1/(k6 + x1))/k66,
  diff(x2, t) = (1*k66*k7*x1 + 1*k66*k9*x3 + (-1)*k66*k10*x2/(k11 + x2) + (-1)*k66*k8*x2)/k66,
  diff(x3, t) = ((-1)*k66*k9*x3 + 1*k66*k8*x2 + (-1)*k66*k12*x3/(k13 + x3))/k66,
  diff(x4, t) = (1*k66*k14*x12^k15/(k16^k15 + x12^k15)*k17^k18/(k17^k18 + x3^k18) + (-1)*k66*k19*x4/(k20 + x4))/k66,
  diff(x5, t) = (1*k66*k21*x4 + 1*k66*k23*x6 + (-1)*k66*((1 - ceiling(sin(pi*t/k65 + 1/1000)/2))*k24 + k25)*x5/(k26 + x5) + (-1)*k66*k22*x5)/k66,
  diff(x6, t) = ((-1)*k66*k23*x6 + 1*k66*k22*x5 + (-1)*k66*((1 - ceiling(sin(pi*t/k65 + 1/1000)/2))*k27 + k28)*x6/(k29 + x6))/k66,
  diff(x7, t) = (1*k66*k30*x6^k31/(k32^k31 + x6^k31) + (-1)*k66*k33*x7/(k34 + x7))/k66,
  diff(x8, t) = (1*k66*k35*x7 + 1*k66*k37*x9 + (-1)*k66*k38*x8/(k39 + x8) + (-1)*k66*k36*x8)/k66,
  diff(x9, t) = ((-1)*k66*k37*x9 + 1*k66*k36*x8 + (-1)*k66*k40*x9/(k41 + x9))/k66,
  diff(x10, t) = (1*k66*(ceiling(sin(pi*t/k65 + 1/1000)/2)*k42*x13 + (ceiling(sin(pi*t/k65 + 1/1000)/2)*k43 + k44)*k45^k48/(k45^k48 + x6^k48))*k46^k47/(k46^k47 + x3^k47) + (-1)*k66*k49*x10/(k50 + x10))/k66,
  diff(x11, t) = (1*k66*k51*x10 + 1*k66*k53*x12 + (-1)*k66*k54*x11/(k55 + x11) + (-1)*k66*k52*x11)/k66,
  diff(x12, t) = ((-1)*k66*k53*x12 + 1*k66*k52*x11 + (-1)*k66*k56*x12/(k57 + x12))/k66,
  diff(x13, t) = (1*k66*(1 - ceiling(sin(pi*t/k65 + 1/1000)/2))*k58 + (-1)*k66*k61*x13/(k59 + x13) + (-1)*k66*k60*ceiling(sin(pi*t/k65 + 1/1000)/2)*x13)/k66 }