cost volume 代价容量函数
cost-volume在计算机视觉中特指计算机视觉中的立体匹配stereo matching问题中的一种左右视差搜索空间
A cost volume stores the data matching costs for associating a pixel with its corresponding pixels at the next frame
In PWC-Net, It uses the warped features and features of the first image to construct a cost volume, which is processed by a CNN to estimate the optical flow
参考：
https://www.zhihu.com/question/297481800
