Pemborosan inventory disebabkan karena tidak adanya koordinasi dalam sistem Supply Chain Management. Koordinasi antara vendor dan buyer dapat mengurangi biaya inventory dalam sistem. Dengan metode joint economic lot size akan ditentukan lot produksi dan lot order yang optimal bagi vendor dan buyer. Dalam penelitian ini juga diusulkan penerapan metode quantity discount. Dari penelitian ini diperoleh nilai lot produksi dan lot order optimal serta nilai quantity discount. Selain itu, diperoleh juga perbandingan besarnya biaya inventory model independen dengan model koordinasi. Pengaruh perubahan parameter terhadap perilaku model diteliti dengan sensitivity analysis terhadap beberapa parameter kunci.

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The problem of inventory loose is caused by non co¬ordination in the Supply Chain Management. Co¬ordination between vendor and buyer could minimize inventory cost in the system. Joint economic lot size method will determined the optimal lot production and lot order for vendor and buyer. This research also propose the quantity discount method. From this research, the joint economic lot size production and order and the value of the quantity discount are obtained. Also, the differences of inventory cost between independent model and co¬ordination model are obtained. Finally, A sensitivity analysis is performed to explore the effect of key parameters.