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# Finance Quant Interview - II

For what values of $$p$$ is

$\begin{pmatrix} 1 & p & 0.6 \\ p & 1 & -0.8 \\ 0.6 & -0.8 & 1 \\ \end{pmatrix}$

a correlation matrix?

Note by Calvin Lin
2 years, 9 months ago

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A correlation matrix must be Symmetric and Positive Semi-Definite and hence all its eigenvalues must be real and non-negative. Writing out the characteristic equation for the above matrix and requiring the above condition yields $-0.96 \leq p \leq 0$

- 2 years, 9 months ago

Apart from trying to bound the roots of the characteristic equation, what other ways can we use?

Staff - 2 years, 9 months ago

Non-negativity of the determinant would yield the same necessary result.

- 2 years, 9 months ago