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Hypersurface

As explained in Math and Architectures of Deep Learning

A surface of arbitrary dimension.

A hypersurface is a surface of arbitrary dimension. In classification, it forms a decision boundary: data points on different sides belong to different classes. In high-dimensional input spaces, the boundary separates clusters of vectors representing classes. section 3.1.2

The boundary's geometry determines how classes are separated:

  • A hyperplane provides a linear separator when class clusters can be divided by a flat boundary. section 3.1.2 section 7.2.2
  • A curved hypersurface, such as a hypersphere, handles more complicated class arrangements that a hyperplane cannot separate. section 3.1.2 section 7.2.2
  • For a boundary described by φ(x) = 0, points with φ(x) = 0 lie on the surface, while positive and negative values identify opposite sides. section 7.2.2

Car–giraffe and horse–zebra classification

Rasterized images become points in a high-dimensional space. Car and giraffe points can be separated with a hyperplane, whereas horse and zebra points may require a curved hypersphere. Training determines the boundary parameters, such as a hyperplane's orientation and position or a hypersphere's center and radius. section 3.1.2

How Math and Architectures of Deep Learning covers it

How deep it goes
Explains geometric intuition, linear and nonlinear forms, and sign-based side assignment, but stops short of training algorithms.
Examples
Uses rasterized car–giraffe and horse–zebra classification examples with hyperplane and hypersphere boundaries.
What it assumes
Assumes input vectors and classifiers, while building intuition from class clusters and two- or three-dimensional geometric analogies.
What you can do after
Evaluate how boundary geometry separates classes and interpret which side of a decision surface contains an input.
How it connects
Connects hypersurfaces to classifiers, decision boundaries, hyperplanes, nonlinear separators, training data, and training.

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.