  Properties of cooperation's probability function in Prisoner`s Dilemma have
impact on evolution of game. Basic model defines that probability of
cooperation depends linearly, both on the player's altruism and the co-player's
reputation. I propose modification of activation function to smooth one
(hyperbolic tangent with scaling parameter a, which corresponds to its shape)
and observe three phases for different range of a. (1) For small a, strategies
seem to randomly change in time and situation of mixed choices (one cooperates
and second defects) dominate. (2) For medium a, players choose only one
strategy for given period of time (the common state can switch to opposite one
with some probability). (3) For large a, mixed strategy (once defect, once
cooperate) is coexisting with common strategies and no change is allowed. I
believe that proposed function characterizes better socio-economical phenomena
and especially phase 1 and 2 contain most of human behavior.
