Request to include FCM loss.

[junyuchen245]

Hi @JunMa11 ,

I greatly appreciate the effort you've put into creating a library of loss functions for the community. I'm reaching out to see if you might consider adding a loss function that we've developed, the FCM loss, which is specifically designed for both unsupervised and semi-supervised registration tasks.
Paper: Medical Physics
Code: FCM Loss

Thank you!
Junyu