Is a Zero Principal Minor in PSD Matrices Indicative of Smaller Zero Minors?

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SUMMARY

The discussion centers on the properties of principal minors in positive semidefinite (PSD) matrices. It is established that the statement "If any principal minor (≠ A) is zero, then all principal minors contained in this minor should also be zero" is incorrect. A counterexample is provided using a diagonal matrix D={1,1,0,1,...}, where A_33=0 while A_22 remains non-zero. The implications of this finding extend to Hermitian matrices, although the discussion does not delve into specifics regarding their properties.

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Hi everyone,
Let A=(a_{ij}) be a symmetric (i.e., over reals) PSD matrix. Then is the following correct?

"If any principle minor ( \ne A ) be zero, then all principle minor contained in this minor should also be zero".

I can not prove or disprove it..any help?

By the way how the result will change if we consider Hermitian matrix (over complex) instead of symmetric matrix?

Thanks
 
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Oh..I got the answer. Its not correct. Consider the diagonal matrix: D={1,1,0,1,...}. Clearly $A_33=0$ but $A_22$ is non-zero.
 

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