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Tangent plane

As explained in Math and Architectures of Deep Learning

A line or direction that touches a curve locally and indicates the direction along which movement leaves a level contour unchanged.

A tangent plane describes directions that remain locally on a level surface, so the function value does not change to first order. For a level contour, the corresponding tangent direction follows the contour; movement perpendicular to it gives the greatest change. The gradient is normal to the tangent surface. section 3.3.2

Use the tangent–normal relationship to interpret loss landscapes:

  • Moving along a tangent direction stays on the same level contour or surface. section 3.3.2
  • Moving along the normal, which is the gradient direction, crosses level surfaces with maximum change. section 3.3.2
  • In model training, these directions describe how parameter movement changes or preserves the loss. section 3.3.2

Circular level contours

For L(w0, w1) = √(w0² + w1²), a level contour is a circle. Moving around its circumference follows the tangent and leaves L unchanged; moving radially follows the normal and changes L most rapidly. section 3.3.2

How Math and Architectures of Deep Learning covers it

How deep it goes
Explains geometric meaning through contours, surfaces, normals, gradients, and directional derivatives without deriving optimization algorithms.
Examples
Uses circular contours, concentric spheres, and coaxial cylinders to illustrate tangent and normal directions.
What you can do after
Evaluate how parameter directions affect a loss by identifying tangent, normal, and gradient directions on level surfaces.
How it connects
Connects tangent directions to level surfaces, gradients, normal vectors, directional derivatives, and loss minimization.

Related concepts

This explainer was generated by Manning's knowledge graph from the text of Math and Architectures of Deep Learning. The section links point to the parts of the book it draws on.