The Problem of Local Optima (C2W3L10) | Summary and Q&A

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August 25, 2017
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DeepLearningAI
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The Problem of Local Optima (C2W3L10)

TL;DR

Deep learning optimization algorithms are more likely to encounter saddle points than local optima in high-dimensional spaces, and plateaus can slow down learning progress.

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Key Insights

  • ❓ Local optima are less of a concern in deep learning optimization than previously believed.
  • 😥 Saddle points, where the derivative is zero in multiple directions, are more common in high-dimensional spaces.
  • 😘 Plateaus, regions with low derivative values, can significantly hinder learning progress.
  • 🐢 Advanced optimization algorithms like momentum or Adam can help overcome slow learning on plateaus.
  • 👾 Understanding high-dimensional spaces in deep learning optimization is still evolving.
  • 😘 Intuition from low-dimensional spaces does not necessarily apply to high-dimensional optimization problems.
  • 😀 Learning algorithms operating with a large number of parameters face unique optimization challenges.

Transcript

in the early days of deep learning people used to worry a lot about the optimization algorithm getting stuck in bad local optima but as the theory of deep learning has advanced our understanding of local optima is also changing let me show you how we now think about local optima and problems in the optimization problem in deep learning so this was ... Read More

Questions & Answers

Q: What was the previous concern regarding deep learning optimization algorithms?

In the early days, people worried about optimization algorithms getting stuck in bad local optima, hindering progress towards global optima.

Q: Are most points with zero gradients in the cost function local optima?

No, most points of zero gradients are actually saddle points in high-dimensional spaces, where the function can curve up or down in different directions.

Q: Why are saddle points more prevalent in high-dimensional spaces?

In high-dimensional spaces, it is less likely for all directions of the function to bend upwards, making saddle points more common than local optima.

Q: What are plateaus in the context of deep learning optimization?

Plateaus are regions where the derivative of the cost function is close to zero for a significant period, leading to flat surfaces and slow learning progress.

Summary & Key Takeaways

  • In deep learning, the concern about getting trapped in bad local optima has evolved, with saddle points being more common in high-dimensional spaces.

  • Most points with zero gradients in the cost function are saddle points rather than local optima, due to the complexity of high-dimensional spaces.

  • Plateaus, where the derivative is close to zero for an extended period, can significantly slow down learning progress.

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