比较两个设计的更改:完成layout设计后，比较网表文件、comp文件，以获得网表的修改信息、器件增删信息、pin的连接更改信息。-compare design changes：after you compelete your layout, use this tool to compare your netlis file and comp file to get those inforamtions about nets change, components changes and pin connection changes.