group_normalization

GN has been implemented by official PyTorch, so I recommend to use the official one which is more memory efficient.

pytorch re-implementation of group normalization in https://arxiv.org/abs/1803.08494

ref:

@article{wu2018group,
    title={Group Normalization},
    author={Yuxin Wu, Kaiming He},
    journal={arXiv preprint arXiv:1803.08494},
    year={2018}