\[\operatorname{tr}(\mathbf{A})=\operatorname{tr}(\mathbf{S}{\mathbf{S}}^{-1}%
\mathbf{A})=\operatorname{tr}({\mathbf{S}}^{-1}\mathbf{A}\mathbf{S})=\sum_{i=1%
}^{n}\lambda_{i}.\]