Quadratic form

Quadratic form is a function expressed as a multivariable equation in linear algebra that has only combined power of two. When represented by matrices, it has a geometric significance as a shift or transformation in coordinates.

A quadratic form q(x) can be written as:

q(x) = x(A x)

where y = A x is the vector resulting from multiplying a matrix and a vector (a linear transformation) and x (y) is the scalar product of vectors.