Momentum is an optimization technique that accumulates an exponentially decaying moving average of past gradients. Updates continue in directions supported by recent gradients, so their size reflects gradient magnitude and alignment. section 10.4
Momentum is characterized by these practical points:
- Use the momentum parameter α to control the moving average; common values are 0.5 and 0.9. section 10.4
- Interpret aligned gradients as reinforcing movement, while the resulting step size depends on the magnitude and alignment of the gradient sequence. section 10.4
- Distinguish Nesterov momentum by evaluating the gradient after applying the current velocity, which adds a correction factor. section 10.4
Optimizer comparison
Compare momentum with stochastic gradient descent, Nesterov momentum, AdaGrad, RMSProp, and Adam when training a LeNet model on CIFAR-100, using cross-entropy loss and validation accuracy. section 10.4





