In this paper, we propose a new approach to obtain flexible taxation of productive commodities from industrial units in a special economic zone (SEZ) based on mathematical models and optimization, that it is generalizable on other trade free zones. For this purpose, we introduced a mathematical model to obtain a goal oriented duties by using partial differential equation and recursive equation. To analyze this model we make a nonlinear programming problem that by it zone manager can study the effects of the proposed model. Finally, we implement this model on a case study to receive taxation of productive commodities into a special economic zone

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