## 2 Methodology
### Setting of Reference Points
#### 2.2.3 Fusion of Two Reference Points  
The \"value function\" and \"decision weights\" together determine the magnitude of the prospect value [26]. Therefore, the prospect value function can be expressed as follows:  
\[V\ =\ \sum\limits_{k\ =\ 1}^{K}\pi(p_{k})\wp(x_{k}). \tag{21}\]The weight function is expressed as follows:  
\[\pi(p)\ =\ \frac{p^{\gamma}}{\left(p^{\gamma}+\left(1-p\right)^{\gamma}\right)^{ \frac{1}{\gamma}}}. \tag{22}\]  
The value function is typically expressed as follows:  
\[v(x)\ =\ \begin{cases}x^{\alpha},&x\geq 0;\\ -\theta(-x)^{\beta},&x<0.\end{cases}  \tag{23}\]  
For the parameters in the above equation, the literature [36] has determined through extensive experiments that \(\alpha\ =\ \beta\ =\ 0.88\) and \(\theta\ =\ 2.25\). For Equation (22), when facing gains, \(\gamma\ =\ 0.61\) and when facing losses, \(\gamma\ =\ 0.69\). The value function has the following three main characteristics [26]:  
1. In practical decision-making, under normal circumstances, decision-makers tend to choose the current situation as the reference point, and the value function is relative to the reference point. When the outcome is perceived as a loss, people generally prefer risk; when the outcome is perceived as a gain, people generally prefer to avoid risk. Therefore, a decision-maker's attitude toward risk is often determined by the specific situation at the time of making the decision and is not fixed or unchanging. 2. The value function curve generally exhibits an \"S\" shape. As shown in Figure 3, it can be observed that when the decision outcome is a gain, decision-makers tend to avoid risk; when the decision outcome is a loss, decision-makers generally seek risk. Additionally, as the gains or losses increase, the value curve gradually levels off, indicating that decision-makers' attitude toward gains or losses follows a principle of diminishing marginal utility. 3. Decision-makers' perception of losses is greater than that of gains. In other words, when people face equal amounts of gain and loss, they tend to feel the loss more intensely. For the above external reference points, the prospect value of each customer's evaluation of each alternative relative to the external reference points is derived. In other words, the prospect values of the alternative solutions relative to the positive and negative reference points are obtained as follows:  
1. When the attribute value is a \"three-parameter interval grey number\", the prospect value is given by \[\left(\left(V_{kji}^{1}(\otimes)\right)_{1}\right)\ =\ v_{kj}^{(+)}\Big{(}u_{kji}^{( \otimes)}\Big{)}\pi_{kj}^{(+)}(p(\otimes))+v_{kj}^{(-)}\Big{(}u_{kji}^{( \otimes)}\Big{)}\pi_{kj}^{(-)}(p(\otimes)),1\leq j\leq y.\] (24)
2. When the attribute value is a \"triangular fuzzy number\", the prospect value is given by  
Figure 3: Value function. \[\Big{(}(V_{kjl}^{2}(\otimes))_{1}\Big{)}\ =\ v_{kj}^{(+)}\Big{(}u_{kji}^{(\otimes)} \Big{)}\pi_{kj}^{(+)}(p(\otimes))+v_{kj}^{(-)}\Big{(}u_{kji}^{(\otimes)}\Big{)} \pi_{kj}^{(-)}(p(\otimes)),y\leq j\leq J. \tag{25}\]  
The prospect value of a single electricity sales package for each attribute is  
\[(V_{kjl}(\otimes))_{1}\ =\ (V_{kjl}^{1}(\otimes))_{1}+(V_{kjl}^{2}(\otimes))_{1}. \tag{26}\]  
Similarly, based on the time reference points derived above, the prospect value of each customer's evaluation of each electricity sales package relative to the time reference points is calculated. The specific formula is as follows:  
1. When the attribute value is a \"three-parameter interval grey number\", the prospect value is given by \[\Big{(}(V_{kjl}^{1}(\otimes))_{2}\Big{)}\ =\ v_{kj}^{(+)}\Big{(}s_{kjl}^{( \otimes)}\Big{)}\pi_{kj}^{(+)}(p(\otimes))+v_{kj}^{(-)}\Big{(}s_{kjl}^{(\otimes )}\Big{)}\pi_{kj}^{(-)}(p(\otimes)),1\leq j\leq y.\] (27)
2.