Why gradients can not be propagated backward to the input proposal coordinates in the RoI pooling layer?

jcjohnson / densecap

Dense image captioning in Torch

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Why gradients can not be propagated backward to the input proposal coordinates in the RoI pooling layer? #78

Open Dorniwang opened 6 years ago

Dorniwang commented 6 years ago

just like what i ask in title, in paper author said "gradients can be propagated backward from the output features to the input features, but not to the input proposal coordinates", i want to know why? thanks.