Can this diagonal matrix be similar to it's negation?

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Suppose I have a diagonal matrix such as
$$ A:= \begin{bmatrix} 1 & 0 & 0 \\ 0 & 1 & 0 \\ 0 & 0 & -1 \\ \end{bmatrix}, $$ Is there a way to find an invertible matrix P, such that: $-A = P^{-1} A P $?

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No.

The existence of such a matrix $P$ would imply that $-A$ is similar to $A$. In particular, this would imply that $$ \DeclareMathOperator{trace}{trace}\trace(A)=\trace(-A) $$ which is of course impossible since $\trace(A)=1$ and $\trace(-A)=-1$.