網址: https://www.researchgate.net/publication/234846101/figure/fig2/AS:668965583998984@1536505232370/Example-of-profile-of-V-and-W-along-a-given-direction-The-inflection-point-of-V.png
網址2: https://www.researchgate.net/figure/Example-of-profile-of-V-and-W-along-a-given-direction-The-inflection-point-of-V_fig2_234846101
