3
$\begingroup$

I am confused about symmetric bilinear forms. Here is my question: Let b is a positive definite symmetric bilinear form on real vector space. Is b non-degenerate?

  • 0
    I think $0$ is usually considered positive-definite in this context.2012-12-23

1 Answers 1

3

Yes. To say that $b$ is non-degenerate is the same as to say that there is no $x$ such that the function $f_x: V \to V$ given by $ y \mapsto b(x, y) $ is identically the zero function.

To say that $b$ is positive definite means that for any $x$, $b(x, x) > 0$. In particular, $f_x(x) = b(x, x) \neq 0$ and so $f_x$ is not identically the zero function.

  • 0
    Isn't there any way to prove that? I am trying to show that is b symmetric bilinear respectively positive,negative and indefinite, b is non-degenerate and controversely while b is non-degenerate is b pos, neg or indefinite?2012-12-23