Bred vectors (BVs) and Lyapunov vectors (LVs)
   are closely related:
BVs with infinitesimal amplitude are identical to
   leading LVs.
BVs are Finite-Amplitude, Finite-Time, whereas
   LVs are infinitesimal, and are defined after
   an infinite time
 Which ones are better for data assimilation and
   ensemble forecasting?