A gradient is a vector of partial derivatives describing how a scalar loss changes with respect to model parameters. For minimization, optimization moves parameters in the gradient’s negative direction. section 10.4
Neural-network optimization uses the gradient to determine parameter updates:
- Stochastic gradient descent computes the loss gradient on a mini-batch and updates parameters using a learning rate. section 10.4
- Momentum accumulates an exponentially decaying average of past gradients, making step size depend on gradient magnitude and alignment. section 10.4
- Nesterov momentum evaluates the gradient after applying the current velocity, adding a correction to the update. section 10.4
- Learning-rate schedules control update size; rates that are too high can miss optima, while rates that are too low prolong training. section 10.4
Training a convolutional network
A CNN trained on CIFAR-100 can compare cross-entropy loss and validation accuracy under different gradient-based optimizers. section 10.4



















