For a quadratic form in the canonical form
the rank is the total number of square terms (both positive and negative).
For a quadratic form in the canonical form
the rank is the total number of square terms (both positive and negative).
Weisstein, Eric W. "Quadratic Form Rank." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/QuadraticFormRank.html