The psd2edm function performs the inverse operation of the edm2psd function,
taking a matrix in \(S_{n-1}^{+}\) and transforming it to a matrix in \(D_{n}^{-}\).
$$psd2edm(S_{n-1}^{+}) = D_{n}^{-}$$
Therefore, psd2edm on \(S_{n-1}^{+}\) is the inverse operator of edm2psd on \(D_{n}^{-}\).
For a symmetric positive semi-definite matrix S, psd2edm(S) will be in \(D_{n}^{-}\).