Knowledge Distillation for Incremental Learning


One of many main areas of concern in deep studying is the generalisation drawback. This has been a sizzling matter for analysis for the previous few years. Typically what occurs is that we get a use case, we construct a mannequin for that and we push it in manufacturing.

However what if we now have a slight change in our drawback assertion? Do we have to remedy it as soon as once more from scratch? What if we do not have the dataset we had beforehand?

We look for a technique to protect the earlier studying of the system and work on simply the evolution half. And we shall be speaking about one of many related features of the issue on this weblog.

So, welcome to the brand new weblog of Study & Share thread, and bear with me for among the subsequent few paragraphs on information distillation for incremental studying.

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Incremental Studying

Allow us to outline the issue assertion first, after which we will talk about the varied options for that.

Suppose you’ve a dataset for five lessons and also you constructed a deep studying community for the classification drawback. Now, allow us to think about you’ve the mannequin, however you misplaced the dataset and it’s good to add an additional class for the present drawback assertion. Effectively, allow us to not get to the answer that shortly. As an alternative, allow us to derive the answer from the historical past itself.

Knowledge Distillation for Incremental Learning

One of many well-known begins within the approaches of generalisation is transfer studying, which has in actual fact proved to be very profitable.

So, on this strategy, we have already got a pre-trained mannequin for a dataset1. Now, with a brand new dataset2, which comes from the same form of area, we are able to use the information of the earlier pre-trained mannequin as an alternative of coaching it once more from scratch.

What occurs is that we initialise the brand new mannequin with the identical weights as of the pre-trained mannequin and add a brand new softmax layer, eradicating the final layer of the earlier mannequin (contemplating it’s a classification drawback). And we prepare the mannequin, ranging from the purpose the place the pre-trained mannequin had reached already. This leads to quick and higher convergence.

If the earlier mannequin could be very giant, we wouldn’t have to replace the weights for its earlier layers (you’ll be able to resolve what number of) by freezing them (making them untrainable). We replace solely the weights of the additional layers (some earlier layers too if you would like) we now have added. This technique is named Advantageous Tuning.

Traditional Machine Learning (ML) vs. Transfer Learning


Try Praphul’s reinforcement studying sequence, which incorporates posts on Q-learning, building a custom environment, deep Q networks, actor-critic networks, and proximal policy optimization (PPO)


Limitations of Switch Studying

The limitation of switch studying is that it can’t be used for incremental studying if we wouldn’t have the dataset for the earlier lessons. 

Confused? 🤔 Allow us to perceive it by an instance: Suppose the pre-trained mannequin used the dataset1 which had lessons -> {A, B, C, D}. Now we have to add some further lessons, allow us to say {E, F, G} to mannequin. The plain strategy could be to take away the earlier softmax layer having four output node, add a brand new one with 7 output nodes, and fine-tune the mannequin with a brand new dataset consisting of lessons -> {E, F, G}. Effectively, when you try this, you’ll get very dangerous accuracy for the earlier lessons (perhaps for the brand new lessons too).

That is the most important drawback we shall be speaking about from right here now, and it’s known as Catastrophic Forgetting by neural networks.


Revise and Study

We, people, are superb at generalisation as a result of we now have some form of reminiscence community in our mind which shops the earlier information and fine-tunes it in keeping with the brand new duties we get uncovered to. The necessary factor is that we don’t deviate a lot from our earlier studying. Neural networks are very primary and easy prototypes of actual neurons, and it nonetheless is difficult to succeed in to that degree.

In our earlier drawback, if we now have the earlier dataset1 and we mix it with the brand new dataset2 to succeed in our ultimate goal, we certainly get a superb outcome. That’s as a result of the dataset1 lets the neural community revise its information and avoids it from deviating an excessive amount of. The dataset2, then again, permits the neural community to fine-tune itself for studying new lessons.

So, is having all the dataset the one resolution? IT IS NOT 😀. Allow us to talk about the doable options one after the other:


A Needed Naive One 👇🏻

Because the identify suggests, it doesn’t go effectively with the efficiency, however nonetheless, it’s good to know the naive ones for attaining a greater resolution.

Keep in mind, we talked about not letting our neural community deviate an excessive amount of. So one apparent factor for that will be so as to add a regularizing constraint on the weights of the pre-trained mannequin to forestall it from going too far.

The explanation it doesn’t work is as a result of, in neural networks, usually we now have extra variety of weights than all the information factors, and thus they study capabilities that are extremely sophisticated and much away from being linear. Even a small quantity of change within the weights might enable the brand new ultimate goal perform to go farther from the previous one.

No worries, have endurance. We’ve a greater resolution coming subsequent👇🏻


Pseudo-Revision 🙄

In case you recall, we talked about revising previous issues earlier than studying the brand new ones. So, the concept right here is to acquire one thing which can be utilized for the revision for our pre-trained mannequin. And that is what a analysis proposed by Zhizhong Li et al does.

The revision half is completed by the dataset2, however with a special technique. Even when a data-point doesn’t belong to the educated lessons, a neural community will predict some chances for every of these lessons. The anticipated chances for the previous lessons act just like the previous labels within the new-training now. The purpose is to acquire the same form of chance distribution which the previous mannequin would have predicted for the brand new dataset2.


Information Distillation-Loss

The loss perform used for the previous activity shall be a modified cross-entropy with the chances altered in keeping with the definition given by Hinton et al. 

The thought right here is to extend the weights for the low chances for the higher encoding of similarities among the many lessons. The loss perform will be mathematically represented as follows:

Knowledge Distillation Loss Function

the place,

Knowledge Distillation Loss

T is a continuing better than or equal to 1. For the brand new duties, we use the standard categorical cross-entropy loss.



Now that we perceive the loss capabilities and the fundamental concept behind the analysis, allow us to talk about the end-to-end algorithm:

Learning Without Forgetting Algorithm

Step 1: Get hold of chances for the previous activity by feeding the dataset2 to the previous mannequin Step 2: Randomly initialise the weights of recent layers that you’ve added.

Throughout coaching we now have three losses:

  1. The loss for previous activity: Lprevious
  2. The loss for brand new activity: Lnew
  3. Regularization for the weights

To manage the significance for the losses, the entire loss is a weighted sum of the three losses talked about above with λprevious as the load for the previous activity loss, λnew as the load for the brand new activity loss, and λr because the regularizer fixed.

The above algorithm provides us good efficiency, however the multi-task switch studying strategy with information for each class stands above once we contemplate efficiency.





I hope the weblog provides an informative perception into incremental studying. I’ll preserve including extra algorithms as I continue learning about them.

Until then, Preserve Studying, Preserve Sharing

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