Tensors - Part 3

Linear Algebra
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Tsakanikas Nickos
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Tensors - Part 3

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Post by Tsakanikas Nickos »

Definition 1: Let $V$ be a finite-dimensional $\mathbb{R}$-vector space and let $k$ be a non-negative integer. A covariant $k$-tensor is a multilinear function $T \ \colon V \times \dots \times V \to \mathbb{R} $.

Definition 2: Let $V$ be a finite-dimensional $\mathbb{R}$-vector space. A 2-tensor $ \omega$ on $V$ is called non-degenerate if the following implication holds:
\[ \omega(X,Y) = 0 \ , \forall Y \in V \implies X = 0 \]


Show that the following are equivalent for a $2$-tensor $\omega$:
  1. $\omega$ is non-degenerate.
  2. The matrix $(\omega_{ij})$ representing $\omega$ in terms of any basis is invertible.
  3. The linear map $ \tilde{\omega} \ \colon V \to V^{*} \ , \ \tilde{\omega}(X)(Y) = \omega(X,Y) $ is non-singular.
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