Change in price will cause the quantity supplied to drop to zero.改變價格的話供應數量將會變成0。
2∞>PES>1, Relative Elastic
【A-Level經濟精講】供給的價格彈性（Price Elasticity of supply）
之前已經給大家講解完了PED, XED和YED，接下來就來講解一下剩下的一個Price Elasticity of supply。PES的內容和PED大同小異，也是需要對定義，基本內容還有不同數值以及圖像做到理解并且熟練記憶，雖然在考試中它的戲份不如PED那么多，但因為比較相似，所以學習起來還是相對簡單的。
PES的定義
PES measures the responsiveness of quantity supplied when there is a change in the price.計算公式為：
% of change in quantity supplied / % of change in the price。這里也重新提一下Law of supply：
When price increases,
quantity supplied increases too;
When price decreases,
quantity supplied decreases too.
因為價格變化和供應數量變化是同向的，
所以除了0，其他PES數值一定會是正數。
以下開始分類討論各個PES value。Change in price leads to more than proportionate change in quantity supplied1PES=∞, Perfectly Elastic
Increase in price will result in more than proportionate decrease in quantity supplied.Decrease in price will result in more than proportionate increase in quantity supplied.
價格上漲將會導致更大幅度的供應數量下跌，
價格下跌將會導致更大幅度的供應數量上漲。
Change in price leads to same percentage change in quantity supplied.1PES=1, Unitary Elastic
Increase in price will result in the same percentage decrease in quantity supplied.
注意，PED中的unitary elastic實際是-1，因為數值都為負數所以省略了負號，PES的unitary elastic是+1，
它可以是任何一條通過P-S圖像原點的一次函數。
Change in price leads to less than proportionate change in quantity supplied.11>PES>0, Relatively Inelastic
Increase in price will result in less than proportionate decrease in quantity supplied.Decrease in price will result in less than proportionate increase in quantity supplied.
價格上漲將會導致更小幅度的供應數量下跌，
價格下跌將會導致更小幅度的供應數量上漲。
2PES=0, Perfectly Inelastic
Increase in price results in no change in quantity supplied.不管怎么改變價格，供應數量始終不變。
跟PED一樣，PES的圖像也是分為五個，對應不同特殊數值或者范圍，可以分類進行記憶，但要注意當PED=1和PES=1時的區別
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