canonical basis for symmetric bilinear forms
If is a symmetric bilinear formover a finite-dimensional vector space
, where the characteristic of the field isnot 2,then we may prove that there is an orthogonal basis such that is represented by
Recall that a bilinear form has a well-defined rank, and denote this by .
If we may choose a basis such that , and , for some integers and ,where .Furthermore, these integers are invariants of the bilinear form.This is known as Sylvester’s Law of Inertia. is positive definite if and only if, . Such a form constitutes a real inner product space
.
If we may go further and choose a basis such that and, where .
If we may choose a basis such that ,
or ;and , where , and is the least positive quadratic non-residue.