analysis of cost variation trends in eoq models under a one-time-only price increasing with fuzzy approach

the planning of production and control of inventory problem is one of most important problems that companies are face with them. some times inattention to uncertainty in these problems causes to increase of costs of inventory control systems. one of the important ways encountering to uncertainty is the widespread of fuzzy sets instead of crisp numbers because in this approach, we can determine model parameters as interval numbers. in this paper, we develop an economic order quantity (eoq) model under a one-time-only price increasing that all variable and parameters are triangular fuzzy numbers, to find out the optimal solution of above model, we use three different methods such as ?-cuts method, vujosevic method (defuzzification of internal parameters before solving model and difuzzification of external parameter after solving model). under first policy, we integrate ?-cuts method and non-linear programming problems method to reach to optimal solution. in first methodology, we use ?-cuts approach and parametric non-linear programming technique simultaneously to attain the membership function of external parameters in primary model. these parameters are reached from internal parameters in two phases maximum and minimum non-linear programming problems and this methodology represents the external parameters as an approximated fuzzy number. under another two policies, we use defuzzification technique via centroid method to attain the crisp numbers. the optimal order policies association with three methods is compared as a benchmark approach and numerical computations shows that efficiency of first method is better than two another methods considerably. in fact the first method chooses the optimal and attractive strategies by membership function allocating to different ?-cuts and gives great information to dms to decide and select the best strategies. there methods have been validated with illustrating numerical example. the important target of this model solution is determination of special ordering range, net costs saving quantity (involving ordering, holding and purchasing cost) and finally we will calculate the time of ordering if net costs saving are positive.