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Pretraining

As explained in Data Without Labels

Pretraining is an initial model-training stage that learns general patterns or representations before adaptation to a specific task.

Pretraining is an initial, typically unsupervised stage that learns useful representations before supervised fine-tuning for a downstream task. In deep belief networks, each layer first learns from the data distribution, preparing weights that can support classification, regression, image recognition, or speech recognition. section 8.13 section 8.9.1

A layer-wise pretraining workflow proceeds as follows:

  • Train the first restricted Boltzmann machine with unlabeled data to capture low-level features. section 8.9.1
  • Use the learned representation as input to the next restricted Boltzmann machine, which learns increasingly abstract features. section 8.9.1
  • Train each layer separately with contrastive divergence, using Gibbs sampling to approximate the log-likelihood gradient. section 8.9.1
  • Fine-tune the complete network with backpropagation and labeled data to reduce prediction error. section 8.9.1

Image or speech recognition

A pretrained deep belief network can learn basic patterns in early layers and more complex features in later layers before supervised fine-tuning for recognition. section 8.13 section 8.9.1

How Data Without Labels covers it

How deep it goes
Explains layer-wise RBM training, contrastive divergence, Gibbs sampling, and subsequent backpropagation-based fine-tuning.
Examples
Uses image recognition, speech recognition, dimensionality reduction, generative modeling, classification, and regression as application examples.
What you can do after
Understand how to sequence unsupervised layer training and supervised fine-tuning when developing deep belief networks.
How it connects
Connects deep belief networks with restricted Boltzmann machines, contrastive divergence, Gibbs sampling, supervised fine-tuning, and overfitting.

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This explainer was generated by Manning's knowledge graph from the text of Data Without Labels. The section links point to the parts of the book it draws on.