Machine Learning Fundamentals · free preview

Adam and Adaptive Learning Rates

Adam keeps two averages of the gradient, one for direction and one for magnitude, and divides the first by the square root of the second so each coordinate gets its own effective step size.

1. Two averages of the gradient

Two averages of the gradient

2. The initialization bias

The initialization bias

3. When the second moment misleads

When the second moment misleads

4. What the second moment does

Adam divides the momentum estimate by the square root of the second-moment estimate. Coordinate ii has seen consistently small gradients and coordinate jj consistently large ones. Which statement describes the relative step sizes, holding everything else fixed?

5. The bias correction at step 1

With β1=0.9\beta_1 = 0.9 and a first gradient g1\mathbf{g}_1, the momentum state is v1=(1−β1)g1\mathbf{v}_1 = (1 - \beta_1)\mathbf{g}_1. The bias correction divides by 1−β111 - \beta_1^{1}, and the corrected estimate v^1\hat{\mathbf{v}}_1 equals ____ in terms of g1\mathbf{g}_1.

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