Activation Functions (C1W3L06) | Summary and Q&A

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August 25, 2017
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DeepLearningAI
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Activation Functions (C1W3L06)

TL;DR

Different activation functions, such as sigmoid, hyperbolic tangent, rectified linear unit (ReLU), and leaky ReLU, have different advantages and disadvantages when used in neural networks.

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Key Insights

  • 🖐️ Activation functions play a vital role in neural network architecture as they determine the output of neurons and introduce nonlinearity.
  • 😚 The sigmoid function, while commonly used, has drawbacks such as a limited range and a gradient close to zero for extreme values.
  • 😚 The hyperbolic tangent function is often a better choice for hidden units due to its range between -1 and 1, resulting in activations closer to zero.
  • 🇦🇪 The rectified linear unit (ReLU) and its variants have gained popularity for their faster learning rates and better optimization properties.

Transcript

when you breach a neural network one of the choices you get to make is what activation functions use independent layers as well as at the output unit of your neural network so far we've just been using the sigmoid activation function but sometimes other choices can work much better let's take a look at some of the options in the forward propagation... Read More

Questions & Answers

Q: What role do activation functions play in neural networks?

Activation functions determine the output of a neuron, introducing nonlinearity into the network, and allowing it to learn complex patterns and relationships.

Q: Why is the sigmoid function not recommended for hidden units?

The sigmoid function, which maps values between 0 and 1, has a gradient close to zero for large or small input values, which can slow down gradient descent and hinder learning in hidden units.

Q: How does the hyperbolic tangent function differ from the sigmoid function?

The hyperbolic tangent function is a shifted and rescaled version of the sigmoid function that maps values between -1 and 1, making it more suitable for hidden units due to the closer-to-zero mean activation values.

Q: What are the advantages of using the rectified linear unit (ReLU) as an activation function?

The ReLU function has a derivative of 1 for positive input values, accelerating learning in neural networks. Its simplicity and better performance make it a popular choice for hidden units.

Q: What is the difference between ReLU and leaky ReLU?

Leaky ReLU is a variant of ReLU that introduces a small slope for negative input values, preventing the zero-gradient issue and potentially improving performance.

Summary & Key Takeaways

  • Activation functions determine the output of a neuron and play a crucial role in neural network architecture.

  • The sigmoid activation function, while commonly used, often has its drawbacks, especially when dealing with hidden units.

  • The hyperbolic tangent function, which is a shifted and rescaled version of the sigmoid function, is often a better choice for hidden units due to its range of values.

  • The rectified linear unit (ReLU) and its variant, the leaky ReLU, are becoming increasingly popular activation functions due to their faster learning rates and better performance.

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