returns to scale and damages to scale in dea with undesirable outputs

Returns to scale is a managerial concept which enables decision makers to determine the decrease or increase in the activity levels of decision making units under their supervision. since, in the real world problems, along with the desirable outputs, the undesirable ones exist, thereby, many methods have been introduced to justify the status of returns / damages to scale. according to what is mentioned above, in this paper, a new method has been introduced which considers the desirable and undesirable outputs at the same time. with this new method, one can determine the type of returns to scale and damages to scale, just by solving one mathematical model.