NFO13018901 Intro Network science14307130355李婧雅 node to compare with. If the neighbor's payoff in this round is higher than itself, the node will copy the neighbors strategy in this round with possibility w, that means in the round, the strategy of nodes with higher payoff are more likely to be copied by the ir neighbors FIG4 A typical subgraph of a scale-free network, where two connected hub nodes are linked to many others having significantly less neighbors[5] At first, because each hub node is surrounded by many cooperative neighbor nodes so its accumulated payoff willl be higher than the small-degree nodes and small-degree nodes will copy the strategy of hub node it connects with. Although now cooperative x has lower payoff than defective y does, because of random choice of strategy comparing, x still has higher payoff than most of small-degree neighbor nodes, x can insist cooperative strategy for a time. As time goes by, the neighbor nodes of x tend to copy x's strategy, so there will be more and more cooperators around x, which contributes to the rise of x's payoff. On the contrary, it means there appears more and more defectors around y and y's payoff will decline and gradually be lower than its neighbor node x. At one moment, y will copy x's strategy and change into cooperator and then y's neighbor nodes will also change into cooperators In the end, cooperation will spread in the whole network and all the hub nodes will choose to cooperate. This means if individual chooses to add up its payoff, the hub nodes in the Ba scale-free network tend to choose cooperation and will affect their neighbor nodes[1] 3.2.2 the spread of defective behaviors in Ba scale-free network Besides, to find how hub nodes effectively resist the invade from defectors, we can analyze the spread of defective behaviors. In the beginning, we set only the node XINFO130189.01 Intro Network Science 14307130355 李婧雅 8 node to compare with. If the neighbor’s payoff in this round is higher than itself, the node will copy the neighbor’s strategy in this round with possibility w, that means in the round, the strategy of nodes with higher payoff are more likely to be copied by their neighbors. FIG. 4 A typical subgraph of a scale-free network, where two connected hub nodes are linked to many others having significantly less neighbors[5] At first, because each hub node is surrounded by many cooperative neighbor nodes, so its accumulated payoff willl be higher than the small-degree nodes and small-degree nodes will copy the strategy of hub node it connects with. Although now cooperative x has lower payoff than defective y does, because of random choice of strategy comparing, x still has higher payoff than most of small-degree neighbor nodes, x can insist cooperative strategy for a time. As time goes by, the neighbor nodes of x tend to copy x’s strategy, so there will be more and more cooperators around x, which contributes to the rise of x’s payoff. On the contrary, it means there appears more and more defectors around y and y’s payoff will decline and gradually be lower than its neighbor node x. At one moment, y will copy x’s strategy and change into cooperator and then y’s neighbor nodes will also change into cooperators. In the end, cooperation will spread in the whole network and all the hub nodes will choose to cooperate. This means if individual chooses to add up its payoff, the hub nodes in the BA scale-free network tend to choose cooperation and will affect their neighbor nodes[1]. 3.2.2 the spread of defective behaviors in BA scale-free network Besides, to find how hub nodes effectively resist the invade from defectors, we can analyze the spread of defective behaviors. In the beginning, we set only the node x