{ x20 = piecewise(0, t < -1, 0, t < 0, 1, t < 120, 1),
  x21 = x20*k35,
  x22 = x1,
  x23 = x2,
  x24 = x3,
  x25 = x4,
  1*k51*x1 + 1*k51*x2 + 1*k51*x3 + 1*k51*x4 + 1*k51*x5 + 1*k51*x7 + 1*k51*x8 + 1*k52*x9 + 1*k52*x10 + 1*k52*x11 + 1*k52*x12 + 1*k52*x13 + 1*k52*x15 + 1*k52*x16 + 1*k52*x17 = k51*k53 + k52*k54,
  1*k51*x6 + 1*k51*x7 + 1*k51*x8 = k51*k55,
  1*k52*x14 + 1*k52*x15 + 1*k52*x16 + 1*k52*x17 = k52*k56 }