Question closed, reopened, closed again, deleted. Please undelete my answer to the question https://math.stackexchange.com/questions/4248118/is-this-proof-correct-for-positive-semidefinite-matrices?...

As GEdgar has pointed out in a comment (which is still here at the time of writing) to your question: Comments are intended to be temporary, to go away after a while. So by all means make them into ...

I also voted to close the question. I did read between the lines, but felt like reading a homework question that the OP has shown no effort. For example, the OP could have said that he had read the ...

Speaking of morality: When I was still a beginner at this site, I tried not to upvote a question that I answered, because the act of upvoting made me feel that I was desperate to seek attention from ...

Admittedly, there are times when changing the accepted answer may annoy someone. Here are some circumstances: When the question is a homework question, the accepted answer is a well written hint and ...

Currently, I don't see any merit in using the "matrices" tag. Tags in MSE are not hierarchical and what should be regarded as "matrices" questions is unclear. Unless every "matrices" question is also ...