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翻訳と辞書　辞書検索 [ 開発暫定版 ] スポンサード リンク Stackelberg game ： ウィキペディア英語版 Stackelberg competition The Stackelberg leadership model is a strategic game in economics in which the leader firm moves first and then the follower firms move sequentially. It is named after the German economist Heinrich Freiherr von Stackelberg who published ''Market Structure and Equilibrium (Marktform und Gleichgewicht)'' in 1934 which described the model. In game theory terms, the players of this game are a ''leader'' and a ''follower'' and they compete on quantity. The Stackelberg leader is sometimes referred to as the Market Leader. There are some further constraints upon the sustaining of a Stackelberg equilibrium. The leader must know ''ex ante'' that the follower observes its action. The follower must have no means of committing to a future non-Stackelberg follower action and the leader must know this. Indeed, if the 'follower' could commit to a Stackelberg leader action and the 'leader' knew this, the leader's best response would be to play a Stackelberg follower action. Firms may engage in Stackelberg competition if one has some sort of advantage enabling it to move first. More generally, the leader must have commitment power. Moving observably first is the most obvious means of commitment: once the leader has made its move, it cannot undo it - it is committed to that action. Moving first may be possible if the leader was the incumbent monopoly of the industry and the follower is a new entrant. Holding excess capacity is another means of commitment. == Subgame perfect Nash equilibrium == The Stackelberg model can be solved to find the subgame perfect Nash equilibrium or equilibria (SPNE), i.e. the strategy profile that serves best each player, given the strategies of the other player and that entails every player playing in a Nash equilibrium in every subgame. In very general terms, let the price function for the (duopoly) industry be $P$; price is simply a function of total (industry) output, so is $P(q\_1+q\_2)$ where the subscript 1 represents the leader and 2 represents the follower. Suppose firm i has the cost structure $C\_i(q\_i)$. The model is solved by backward induction. The leader considers what the best response of the follower is, i.e. how it ''will'' respond once it has observed the quantity of the leader. The leader then picks a quantity that maximises its payoff, anticipating the predicted response of the follower. The follower actually observes this and in equilibrium picks the expected quantity as a response. To calculate the SPNE, the best response functions of the follower must first be calculated (calculation moves 'backwards' because of backward induction). The profit of firm 2 (the follower) is revenue minus cost. Revenue is the product of price and quantity and cost is given by the firm's cost structure, so profit is: $\backslash Pi\_2\; =\; P(q\_1+q\_2)\; \backslash cdot\; q\_2\; -\; C\_2(q\_2)$. The best response is to find the value of $q\_2$ that maximises $\backslash Pi\_2$ given $q\_1$, i.e. given the output of the leader (firm 1), the output that maximises the follower's profit is found. Hence, the maximum of $\backslash Pi\_2$ with respect to $q\_2$ is to be found. First differentiate $\backslash Pi\_2$ with respect to $q\_2$: :$\backslash frac\; =\; \backslash frac\; \backslash cdot\; q\_2\; +\; P(q\_1+q\_2)\; -\; \backslash frac.$ Setting this to zero for maximisation: :$\backslash frac\; =\; \backslash frac\; \backslash cdot\; q\_2\; +\; P(q\_1+q\_2)\; -\; \backslash frac=0.$ The values of $q\_2$ that satisfy this equation are the best responses. Now the best response function of the leader is considered. This function is calculated by considering the follower's output as a function of the leader's output, as just computed. The profit of firm 1 (the leader) is $\backslash Pi\_1\; =\; P(q\_1+q\_2(q\_1)).q\_1\; -\; C\_1(q\_1)$, where $q\_2(q\_1)$ is the follower's quantity as a function of the leader's quantity, namely the function calculated above. The best response is to find the value of $q\_1$ that maximises $\backslash Pi\_1$ given $q\_2(q\_1)$, i.e. given the best response function of the follower (firm 2), the output that maximises the leader's profit is found. Hence, the maximum of $\backslash Pi\_1$ with respect to $q\_1$ is to be found. First, differentiate $\backslash Pi\_1$ with respect to $q\_1$: :$\backslash frac\; =\; \backslash frac\; \backslash cdot\; \backslash frac\; \backslash cdot\; q\_1\; +\backslash frac\; \backslash cdot\; q\_1+\; P(q\_1+q\_2(q\_1))\; -\; \backslash frac.$ Setting this to zero for maximisation: :$\backslash frac\; =\; \backslash frac\; \backslash cdot\; \backslash frac\; \backslash cdot\; q\_1+\backslash frac\; \backslash cdot\; q\_1\; +\; P(q\_1+q\_2(q\_1))\; -\; \backslash frac=0.$ 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Stackelberg competition」の詳細全文を読む スポンサード リンク 翻訳と辞書 : 翻訳のためのインターネットリソース Copyright(C) kotoba.ne.jp 1997-2016. All Rights Reserved.