MHB Proving Positive Definite Scalar Product for $n \times n$ Matrices

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To prove that the scalar product defined as $\langle X, Y \rangle = tr(X Y^T)$ is positive definite for $n \times n$ matrices, one must demonstrate that $\langle X, X \rangle \geq 0$ and $\langle X, X \rangle > 0$ if $X \neq 0$. The trace of a matrix, which sums its diagonal elements, plays a crucial role in these proofs. By showing that the trace of a product of a matrix with its transpose is non-negative, one can establish the first property. The second property follows from the fact that if $X$ is non-zero, the product $X Y^T$ will also yield a non-zero trace. Understanding these properties is essential for confirming the positive definiteness of the scalar product.
rputra
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Consider $X, Y$ as $n \times n$ matrices, I am given this definition of scalar product:
$$\langle X, Y \rangle = tr(X Y^T),$$
and I need to prove that it is positive definite scalar product. Of several properties I need to prove, two of them are
(1) $\langle X, X\rangle \geq 0$ and
(2) $\langle X, X\rangle > 0$ if $X \neq 0.$
I am lost on proving these two properties, any help or hints to prove them would be very much appreciated. Thank you before hand for your time and effort.
 
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Hi Tarrant,

A good place to start would be with the definition of the trace for an $n\times n$ matrix. Do you recall what this was?
 

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