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Questions about the properties of vector spaces and linear transformations, including linear systems in general.

56 votes

real symmetric matrix has real eigenvalues - elementary proof

How about Jacobi's proof? See, e.g., Folkmar Bornemann, ``Teacher's Corner - kurze Beweise mit langer Wirkung,'' DMV-Mitteilungen 3-2002, Seite 55 (in German, sorry). Sorry, I don't have the original …
Omar Antolín-Camarena's user avatar
3 votes
Accepted

Schur complement and negative definite matrices

This should be a comment, but I can not yet post comments. You got Schur's complement lemma wrong, the matrix $$\left(\begin{array}{cc} 1 & 1 \newline 1 & -1 \end{array}\right)$$ satisfies you condit …
Uwe Franz's user avatar
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