  A quantum master equation of the Lindblad form is obtained in this paper by
considering the spontaneous wave-packet reduction. Different classical
equations can be derived after exactly mapping such a quantum master equation
to a continuous time random walk (CTRW). Although this CTRW is a quasiclassical
walk, the effects due to the quantum interference can still be important in
such a walk. Macroscopically, we shall consider the uncertainty of the
potential and determine the effective transition probability by a family of
Schr\"{o}dinger equations (or operators).
