Triplet loss

[eli-osherovich]

This PR implements the triplet loss layer.

[cbalint13]

@eli-osherovich

• FYI: CNN Triplet Tranining #3123

[shaibagon]

I see there is very little documentation in the code on how this loss works. If someone wish to understand it better (s)he might find this SO thread useful.

@eli-osherovich, thank you for implementing this loss.

[eli-osherovich]

@shelhamer Is there any interest in this PR? If so, I can add documentation and examples.

[afshindn]

@eli-osherovich Are you planning on adding the examples and documentations?

[BeSlower]

Could you add one example and more documentations? Your code is very helpful for me, but a little bit hard to go through all things.

[jibweb]

@eli-osherovich Nice code, one question though, maybe I'm missing something obvious, but why is the line 65 of triplet_loss_layer.cpp
const Dtype scale = top[0]->cpu_diff()[0] / bottom[0]->num()

If I understood correctly, top[0]->cpu_diff()[0] would be the loss value, so why use this and not just 2 as in the derivation process ?

[kwin-wang]

@jibweb top[0]->cpu_diff[0] is equal to the loss_weight of loss layer in training prototxt file, the default value is 1. it's useful to multi-task learning.

[PeterouZh]

Hi, I want to know why I can't find triplet_loss_layer files in caffe's code now. I'll very thanks if anyone can help me.

[shaibagon]

@pengzhou93 you cannot find files, because this PR was not merged yet. If you want to use it (at your own risk) you can pull this branch.

[soulslicer]

How does this vary from:

#5019

This one looks more extensive