Enhancement of cooperation by giving high-degree neighbors more help

In this paper, we study the effect of preferential assistance on cooperation in the donation game. Cooperators provide benefits to their neighbors at some costs. Defectors pay no cost and do not distribute any benefits. The total contribution of a cooperator is fixed and he/she distributes his/her contribution unevenly to his/her neighbors. Each individual is assigned a weight that is the power of its degree, where the exponent a is an adjustable parameter. The amount that cooperator i contributes to a neighbor j is proportional to j's weight. Interestingly, we find that there exists an optimal value of alpha (which is positive), leading to the highest cooperation level. This phenomenon indicates that, to enhance cooperation, individuals could give high-degree neighbors more help, but only to a certain extent.