2.2.1. Basic Assumptions of the Evolutionary Game Model
- (1)
Game player hypothesis
According to the intention of express companies to participate in joint distribution, express companies N will produce
situations, which can be regarded as an evolutionary game between two factions of competition and cooperation regardless of the choice. When three express delivery companies participate in the alliance game, the final possible results are that none of the three cooperate, two of the three cooperate, and all three cooperate. When all three companies cooperate, their game can be interpreted as the game between any two cooperative alliances and the third company, which can still be regarded as a game between the two parties. Similarly, when four express companies participate in the game, the final possible results are that the four do not cooperate, any two cooperate, any three cooperate or all four cooperate, and this process can be regarded as a game between the alliance that has been built and another alliance or company, and so on, and eventually can be regarded as the evolutionary game between the two sides. The two sides of the game may be a game between the small alliance and the small alliance, or a game between the small alliance and the express company, or a game between the express company and the express company. Therefore, in order to simplify the discussion of the model, go to the center of the problem and make the initial evolutionary game model accurate and conducive to calculation; this paper will therefore study the evolutionary game of both sides. Express companies M and N have bounded rationality, which is biased due to strategic misjudgment. Under the condition that complete information is not required, the game process of both sides is complicated, and the dynamic game equilibrium is reached through continuous trial and error [
48].
- (2)
Behavioral strategy of the game
When the game is played, express companies M and N can only choose between competition or cooperation. Their strategy set is
. If express company M chooses cooperation probability
), then competition probability is
; if express company N chooses cooperation probability
), then competition probability is
[
49].
- (3)
Policy selection and parameters
The equation parameters are defined in
Table 1.
Hypothesis 1. The existence and evolution of excess returns is fundamental in the joint distribution system formed by express companies. Assume that the excess return in the joint distribution system during t is, the distribution coefficient of the excess return of express company M is, and the excess return is; similarly, the distribution coefficient of enterprise N is, and the excess return is.
Hypothesis 2. The implementation of joint distribution between express delivery enterprises can create positive effects for participants, namely,.
Hypothesis 3. The risk cost of cooperative operation is proportional to the total cost. Calculated by the proportional algorithm, the risk cost of cooperative operation is, andbelongs to the interval.
Hypothesis 4. Both express company M and N are considered as finite rational economic agents. Therefore, for the default penalty cost to achieve the desired effect, it needs to meet; the input cost is greater than the penalty cost.
Based on the above assumptions, the evolutionary income payment matrix between rural express joint distribution enterprises is shown in
Table 2 [
50,
51]:
2.2.3. Stability Analysis of the Evolutionary Game Model
According to the basic definition of evolutionary game theory, both sides of the game achieve the stability of the game result by constantly adjusting their strategies and pursuing the final evolutionary stability strategy; namely, the requirements are and first-order derivative .
- (1)
Analysis on the evolutionary stability of the selection strategy of express delivery company M
Let
, solve
Find the first order derivative for
:
At the time
,
. When express company N chooses cooperation probability
, no matter what value express company M chooses for competition probability, the result is Nash equilibrium. Its phase diagram is shown in
Figure 2a.
At the time , according to the conditions given in hypothesis 4: , therefore , which is constant. Therefore, the size of is explored and classified.
When
,
holds; when
, then
; when
, then
. Therefore, according to the stability principle,
is a stable solution. In this case, when the value of excess earnings obtained by express company M after joint distribution is less than the betrayal cost of joint distribution, no matter what strategy express company N chooses, M only chooses the competitive strategy, and its phase diagram is shown in
Figure 2b.
When
,
still holds, as well as the solution of
. Similarly, when the value of excess earnings obtained by express company M after joint distribution is less than the betrayal cost of joint distribution, no matter what strategy express company N chooses, M only chooses the competitive strategy, and its phase diagram is shown in
Figure 2c.
When , it is necessary to make a classification discussion again.
When , then , the is a stable solution, and the final result of the evolutionary game is that express company M chooses a competitive strategy. When , then , the is a stable solution, and the final result of the evolutionary game is that express company M only chooses the cooperation strategy.
According to the classification discussion, in order for express company M to participate in the joint distribution system, the prerequisite is that the value of excess earnings obtained by express company M after joint distribution is greater than the betrayal cost of the joint distribution. At this time, M’s cooperation intention depends on Company N.
- (2)
Evolutionary stability analysis of the selection strategy of express delivery Company N.
Let
, solve
Take the first derivative with respect to phi
At that time,
and
; when express company N chooses cooperation probability
, no matter what value express company M chooses for competition probability, the result is the Nash equilibrium, and its phase diagram is shown in
Figure 3a.
At that time, , according to the conditions given in Hypothesis 4: ; therefore, , and it is constant, so the size is explored and the classification is discussed.
When
, at this time,
holds; when
, then
; when
, then
. Therefore, according to the stability principle,
is a stable solution. In this case, when the value of excess earnings obtained by express company N after joint distribution is less than the betrayal cost of joint distribution, no matter what strategy is chosen by express company M, company N only chooses the competitive strategy, and its phase diagram is shown in
Figure 3b.
When
, at this time,
holds, and the solution of
. Similarly, when the value of excess earnings obtained by express company N after joint distribution is less than the betrayal cost of joint distribution, no matter what strategy is chosen by express company M, company N only chooses the competitive strategy, and its phase diagram is shown in
Figure 3c.
When , then you need to make a classification discussion.
When , then , the is a stable solution, and the final result of the evolutionary game is that express company N chooses the competitive strategy. When , then , the is a stable solution, and the final result of evolutionary game is that express company N only chooses the cooperation strategy.
According to the classification discussion, in order for express company N to participate in the joint distribution system, the prerequisite is that the value of excess earnings obtained by express company N after joint distribution is greater than the betrayal cost of joint distribution. At this time, N’s cooperation intention depends on Company M.
- (3)
Stability analysis of two-dimensional continuous dynamic system of express Company M and express Company N
According to the stability analysis of the two sides of the game, five local equilibrium points are obtained:
The stability of local equilibrium points can be judged by using the method of the Yakerby matrix. The Accord matrix can be obtained by taking partial derivatives with respect to
and
respectively.
Among them
If the express company of M and N are at the end of the game system with the evolution of joint distribution accord, the determinant of a matrix is:
The trace of the Accord ratio matrix of the end-joint distribution evolutionary game system composed of express companies M and N is:
When the determinant of the Accord ratio matrix of the common distribution game system composed of express companies M and N is greater than 0—that is, detJ > 0—and the trace of the determinant is less than 0—that is, trJ < 0—the corresponding local equilibrium point is ESS. The stability of the five local equilibrium points can be judged by respectively substituting them into the formula. The results are shown in
Table 3.
As can be seen from the table, the local equilibrium point
is an evolutionarily stable strategy, that is, the final evolution result of the terminal joint distribution evolutionary game system composed of express companies M and N is either (cooperation, cooperation) or (competition, competition), thus both parties either choose the cooperation strategy or both parties choose the competition strategy. This indicates that one express company chooses the competitive strategy, and the other one will eventually also choose the competitive strategy. In order to achieve joint distribution, the two express companies need to choose the cooperation strategy at the same time. As can be seen from the table, the local equilibrium point
and
are the unstable, and
is saddle point. Therefore, the evolutionary game phase of the terminal joint distribution evolutionary game system composed of express company M and N is shown in
Figure 4.
According to the phase diagram of the evolutionary game, when the initial willingness of express companies M and N fall on the plane composed of , , , , the final result of the evolutionary game will be that both express companies choose a competitive strategy. When the initial willingness of express companies M and N falls on the plane composed of, , , , the final result of the evolutionary game will be that both express companies choose a cooperative strategy.