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Net2Net: Accelerating Learning via Knowledge Transfer (1511.05641v4)

Published 18 Nov 2015 in cs.LG

Abstract: We introduce techniques for rapidly transferring the information stored in one neural net into another neural net. The main purpose is to accelerate the training of a significantly larger neural net. During real-world workflows, one often trains very many different neural networks during the experimentation and design process. This is a wasteful process in which each new model is trained from scratch. Our Net2Net technique accelerates the experimentation process by instantaneously transferring the knowledge from a previous network to each new deeper or wider network. Our techniques are based on the concept of function-preserving transformations between neural network specifications. This differs from previous approaches to pre-training that altered the function represented by a neural net when adding layers to it. Using our knowledge transfer mechanism to add depth to Inception modules, we demonstrate a new state of the art accuracy rating on the ImageNet dataset.

Citations (639)

Summary

  • The paper introduces function-preserving transformations that transfer learned knowledge from a smaller teacher network to a larger student network.
  • Methodologies Net2WiderNet and Net2DeeperNet expand network width and depth, significantly reducing training time while maintaining accuracy.
  • Empirical evaluation on ImageNet with Inception models achieved up to 78.5% validation accuracy, demonstrating practical scalability.

Overview of Net2Net: Accelerating Learning via Knowledge Transfer

The paper Net2Net: Accelerating Learning via Knowledge Transfer by Chen, Goodfellow, and Shlens introduces novel methodologies for efficiently transferring knowledge from one neural network to another, effectively enhancing the training speed of larger neural architectures. The focal point of this research is the reduction of time-intensive training processes commonly associated with neural network optimization.

Concept and Purpose

The principal feature of the Net2Net methodology lies in its use of function-preserving transformations, allowing a student network to inherit the learned knowledge of a smaller teacher network. This approach fundamentally differs from conventional pre-training methods by maintaining the function represented by the network when layers are added. Such innovations are particularly essential in two proposed techniques: Net2WiderNet and Net2DeeperNet.

  • Net2WiderNet expands a network by increasing the width (i.e., number of units) of its layers without altering the function.
  • Net2DeeperNet augments the depth of the network by incorporating new functional layers that maintain the existing transformation.

Empirical Evaluation

The paper presents empirical evaluations on ImageNet using Inception network architectures. Noteworthy findings are demonstrated in several experimental setups:

  1. Net2WiderNet rapidly accelerates training by transforming narrower networks into the standard width, maintaining accuracy levels while significantly reducing convergence time.
  2. Net2DeeperNet enables deeper networks to inherit pre-trained knowledge, offering faster convergence compared to networks trained from scratch.
  3. The final experiment illustrates the utility of these transformations in exploring architectural design space, achieving a remarkable improvement with a validation set accuracy of 78.5% on ImageNet.

Methodological Insights

These transformations offer several methodological advantages:

  • They ensure a larger student network immediately achieves equivalent baseline performance.
  • Changes are guaranteed as improvements, so long as individual steps enhance the model.
  • All parameters remain optimizable, avoiding the necessity to freeze any layers.

Practical and Theoretical Implications

Practically, Net2Net has significant implications for optimizing machine learning workflows, especially in contexts demanding repeated and iterative model training. Theoretically, this research opens pathways for developing more comprehensive transfer learning techniques applicable beyond simple architectural transformations. Future extensions could explore more generalized transformations that transcend architectural constraints between teacher and student networks.

Conclusion and Future Directions

In conclusion, the Net2Net framework represents a significant advancement in accelerating the training processes of neural networks through knowledge retention techniques. The discussion suggests a potential for further investigations into knowledge transfer methodologies that accommodate a broader range of architectural variability. Such endeavors could further optimize the utility of neural networks in increasingly complex and data-rich environments.