Adam

The learning rate is controlling the size of the update steps along the gradient. This parameter sets how much of the gradient you update with, where 1 = 100% but normally you set much smaller learning rate, e.g., 0.001.

In our rolling ball analogy, we’re calculating where the ball should roll next in discrete steps (not continuous). How long these discrete steps are is the learning rate.

Choosing a good learning rate is important when training a neural network. If the ball rolls carefully with a small learning rate we can expect to make consistent but very small progress (this corresponds to having a small learning rate). The risk though is that the ball gets stuck in a local minima not reaching the global minima.

We could also choose to take long confident discrete steps in an attempt to descend faster and avoid local minima, but this may not pay off. At some point, calculating too seldom gives a higher loss as we “overstep”, we overshoot the minima.

The value here defines the process of gradually decreasing the learning rate during training, in order to help speed up its steps along the gradient.

These settings are for optimizer Adam, Adamax, AMSgrad and Nadam. This settings adjust the exponential decay avarage parameters, that are used by the optimizer to gain momentum.

Standard momentum blindly accelerates down slopes, it first computes gradient, then makes a big jump. Nesterov momentum is a way to “look ahead”. It first does a big jump in the direction of the previously accumulated gradient. Then it measures where it ends up and makes a correction resulting in the complete update vector.