Research Article
Research on Hub-and-Spoke Transportation Network of China Railway Express
Table 4
The variables in the SOS2 model.
| Parameter | Descriptions |
| l | Breakpoint index of the convex piecewise linear function | | Transportation cost between hubs by considering the scale economy effect | | Flow breakpoint parameter corresponding to the cost and it represents the independent variable breakpoint of the piecewise linear function | | SOS2 variable |
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