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Time Series with PyTorch
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On the surface, it may seem similar to unsupervised learning, but what is special is that we are creating a supervised learning problem from the data itself and generating representations for downstream tasks, which opens more doors compared to traditional unsupervised learning methods. In a review work, Self-Supervised Learning for Time Series Analysis: Taxonomy, Progress, and Prospects, Kexin Zhang and colleagues categorize self-supervised learning into three main categories: generative methods, contrastive methods, and adversarial methods.

Figure 18.1: Examples of contrastive method and reconstruction method
The left panel shows an augmentation-based contrastive method, where we simply reversed and flipped the time series, and constructed a new time series that should be different from the original one, creating contrast. The right panel shows the idea of reconstruction, where we apply a model to reconstruct the time series. Note that these...