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Softmax

As explained in Data Without Labels

A softmax function converts multiple real-valued outputs into nonnegative values that sum to one, typically representing class probabilities.

Softmax converts a neural network’s final outputs into probabilities for multiple classes. These nonnegative values sum to one, making the largest value the predicted class. section 8.2.4 section 8.6.1

Use softmax when:

  • A neural network performs multiclass classification. section 8.2.4
  • The final layer must express competing class predictions as probabilities. section 8.2.4 section 8.6.1
  • A convolutional neural network passes extracted image features through a fully connected layer to its classification output. section 8.6.1

Image classification

For an image classified as a car, bike, or truck, softmax produces one probability for each category; the highest probability determines the prediction. The same pattern applies to cat-versus-dog classification. section 8.2.4 section 8.6.1

How Data Without Labels covers it

How deep it goes
Defines probability output and prediction selection, but does not detail the mathematical formula or implementation procedure.
Examples
Uses car-bike-truck and cat-dog image classification examples to show competing class probabilities.
What it assumes
Assumes familiarity with neural-network layers and classification while placing softmax after learned feature extraction.
What you can do after
Evaluate multiclass neural-network outputs by selecting the class with the highest softmax probability.
How it connects
Connects softmax with activation functions, neural networks, fully connected layers, convolutional neural networks, and multiclass classification.

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