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I know that for a hermitian matrix to be PSD it is necessary that every principal minor [i.e, the minors obtained by deleting all the last i rows and columns for all i=(n-1)(-1)0].

I want to know if it is necessary that all minors of order>=2 be non-negative.

Particularly, for the 4x4 hermitian matrix

a_11 a_12 a_13 a_14

a_21 a_22 a_23 a_24 (please read it as a matrix)

a_31 a_32 a_33 a_34

a_41 a_42 a_43 a_44

is it necessary that the minors

a_11 a_13

a_31 a_33

and

a_22 a_24

a_42 a_44

should be non-negative?

Please help.

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# Condition on minors to be Positive Semidefinite (PSD)

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