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
