微观经济学赵耀辉第28章(编辑修改稿)

微观经济学赵耀辉第28章(编辑修改稿)内容摘要：

plays second. (U,L) is a Nash equilibrium. (D,R) is a Nash equilibrium. Which is more likely to occur? A Sequential Game Example U D L L R R (3,9) (1,8) (0,0) (2,1) A B B A plays first. B plays second. If A plays U then B plays L。 A gets 3. A Sequential Game Example U D L L R R (3,9) (1,8) (0,0) (2,1) A B B A plays first. B plays second. If A plays U then B plays L。 A gets 3. If A plays D then B plays R。 A gets 2. A Sequential Game Example U D L L R R (3,9) (1,8) (0,0) (2,1) A B B A plays first. B plays second. If A plays U then B plays L。 A gets 3. If A plays D then B plays R。 A gets 2. So (U,L) is the likely Nash equilibrium. Fight Don’t fight Enter Stay out (1,9) (1,9) (0,0) (2,1) Entrant Incumbent Incumbent Don’t fight Fight Entrant plays first. Incumbent plays second. A Game of Entry Deterrence Fight Don’t fight Enter Stay out (1,9) (1,9) (0,0) (2,1) Entrant Incumbent Incumbent Don’t fight Fight IF the entrant stays out, then payoff is (1,9). A Game of Entry Deterrence Fight Don’t fight Enter Stay out (1,9) (1,9) (0,0) (2,1) Entrant Incumbent Incumbent Don’t fight Fight (Enter, Don’t Fight) is a Nash equilibrium. A Game of Entry Deterrence The entrant prefers (Enter, Don’t Fight), but the incumbent may threat to fight. Is the threat credible? Can make it credible. A Game of Entry Deterrence Fight Don’t fight Enter Stay out (1,9) (1,9) (0,2) (2,1) Entrant Incumbent Incumbent Don’t fight Fight By building up excess capacity, the threat bees credible. The potential entrant stays out. A Game of Entry Deterrence Pure Strategies • In all previous examples, players are thought of as choosing to play either one or the other, but no bination of both。 that is, as playing purely one or the other. • The strategies presented so far are players’ pure strategies （ 纯粹策略） . • Consequently, equilibria are pure strategy Nash equilibria. • Must every game have at least one pure strategy Nash equilibrium? Pure Strategies Player B Player A Here is a new game. Are there any pure strategy Nash equilibria? (1,2) (0,4) (0,5) (3,2) U D L R Pure Strategies Player B Player A Is (U,L) a Nash equilibrium? (1,2) (0,4) (0,5) (3,2) U D L R Pure Strategies Player B Player A Is (U,L) a Nash equilibrium? No. Is (U,R) a Nash equilibrium? (1,2) (0,4) (0,5) (3,2) U D L R Pure Strategies Player B Player A Is (U,L) a Nash equilibrium? No. Is (U,R) a Nash equilibrium? No. Is (D,L) a Nash equilibrium? (1,2) (0,4) (0,5) (3,2) U D L R Pure Strategies Player B Player A Is (U,L) a Nash equilibrium? No. Is (U,R) a Nash equilibrium? No. Is (D,L) a Nash equilibrium? No. Is (D,R) a Nash equilibrium? (1,2) (0,4) (0,5) (3,2) U D L R Pure Strategies Player B Player A Is (U,L) a Nash equilibrium? No. Is (U,R) a Nash equilibrium? No. Is (D,L) a Nash equilibrium? No. Is (D,R) a Nash equilibrium? No. (1,2) (0,4) (0,5) (3,2) U D L R More Examples Matching Pennies Player B Player A (1,1) (1, 1) (1,1) (1, 1) H T H T More Examples 点球 进攻球员 守门员 (1,0) (0, 1) (0,1) (。