Towards understanding of the inclusive vs exclusive puzzle in the $\mathrm{\mid }{V}_{cb}\mathrm{\mid }$ determinations

Lattice calculation may play an important role to understand the cause of the long-standing puzzle among the determination of $\mathrm{\mid }{V}_{cb}\mathrm{\mid }$. The key element is the computation of the inclusive decay rate, for which the formalism is under development. The method has its own problem: the approximation of the phase-space factor and finite volume effect. I discuss the current status of such study and future prospects.