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Hi could you help me with following

$$ \begin{pmatrix} 1 & a & a \\ a & 1 & a \\ a & a & 1 \end{pmatrix} $$

is a $3 \times 3$ matrix.

Find the largest interval for a such that this matrix is positive definite.

How to do this??

Thanks a lot!

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    What have you tried? Where did you get stuck? Do you have any thoughts on the problem?2012-12-28

3 Answers 3