{ diff(x1, t) = (-1)*k31*k29*exp(k30*t)*x1/k31,
  diff(x2, t) = ((-1)*k31*k29*exp(k30*t)*x2 + 1*k31*k29*exp(k30*t)*x1)/k31,
  diff(x3, t) = (1*k31*k29*exp(k30*t)*x2 + (-1)*k31*k29*exp(k30*t)*x3)/k31,
  diff(x4, t) = (1*k31*k29*exp(k30*t)*x3 + (-1)*k31*k29*exp(k30*t)*x4)/k31,
  diff(x5, t) = (1*k31*k29*exp(k30*t)*x4 + (-1)*k31*k29*exp(k30*t)*x5)/k31,
  diff(x6, t) = (1*k31*k29*exp(k30*t)*x5 + (-1)*k31*k29*exp(k30*t)*x6)/k31,
  diff(x7, t) = (1*k31*k29*exp(k30*t)*x6 + (-1)*k31*k29*exp(k30*t)*x7)/k31,
  diff(x8, t) = (1*k31*k29*exp(k30*t)*x7 + (-1)*k31*k29*exp(k30*t)*x8)/k31,
  diff(x9, t) = 1*k31*k29*exp(k30*t)*x8/k31 }