$S_c$	Occupied space by storing per PPE c (m3)
${Caps}_{ict}$	The maximum amount produced PPE c by MSM i in period t
${Capd}_j$	The capacity of distributors j (m3)
${WD}_{wct}$	The maximum donation of PPE c by world donator w in period t
${VA}_{hct}$	The number of donated PPE c by voluntary in period $t$ to medical center h
${CDH}_{jhc}$	Transportation cost of PPE c from distributors $j$ to medical center h
${CMD}_{ijc}$	Transportation cost of PPEc from MSM i to distributors j
${CMD}_{wjc}$	Transportation cost of PPE c from world donator $w$ to distributors j
${hd}_{jc}$	Inventory holding cost for PPE c charged by distributor j
${PC}_{cit}$	The procurement cost for PPE c charged by supplier i in period t