Determine the most productive scale of a production unit using a two-stage process based on the demand level

In the real world, there are decision-making units in which the production process can be considered as a two-stage or multi-stage process. In order to evaluate these types of units, the network data envelopment analysis method is used. In this paper, Two-stage units have been investigated, which in the two-stage process are the outputs of the first stage of the second stage inputs, which are referred to as "middle sizes".
The purpose of this research is to determine the most effective scale of the production unit scale using a two-step process based on the demand level.
In this regard, while determining the units of MPSS with ordinary DEA methods, we will generalize it in two-stage models.
Then, the maximum and minimum amount of production, the production units that are in the most efficient scale of the scale, are obtained at each of the stages separately and then generalized for the whole process.
We consider supply and demand as two output indicators and we determine the demand level for each step separately and then the whole process so that we can obtain the maximum and minimum amount of demand.