Hi,
I would like to know if it is possible to use Indices returned by AdaptiveMaxPool to feed into FC layers (not for Unpool) ?
The idea is to provide to the network what features is present, but also where is it. That may help for Embedding or Metric learning ?
Is this a crazy idea ?
I don’t think any idea is too crazy to run some experiments. 
Note that the returned indices from this pooling layer are “detached”, i.e. they do not have a grad_fn and thus Autograd won’t backpropagate through them, so you should keep this information in mind when experimenting with it.
That what I am afraid of: the indice returned do not have grad_fn
Does this mean that backward will have some weird effect ? Would there be any trick to have the indices “attached” ?
Not directly, since you won’t be able to calculate gradients for these indices (unless you can come up with a valid backward method to do so and would implement it manually). Autograd will properly backpropagate to the max. values, but not the indices.