The general mathematical problem of optimal stopping corresponding
to this maintenance problem can be found in [20,10,11].
It is now briefly recalled. Let z ¼ ðk0,y0Þ be the starting point of the
PDMP ðXtÞ. Let Mf be the set of all stopping times t for the natural
filtration of the PDMP (Xt) satisfying trTf that is to say that the
intervention takes place before the time Tf ¼ 1000 h. It has been
shown in previous studies that by 1000 h, all the units are stuck
and the events of interest have been observed, see e.g. [1–4]. Let g
be the cost function to optimize. Here, g is a reward function that
has to be maximized. The optimization problem to solve is given
in Eq. (7)