Show that if $\mathbf{u}(t)$ is a solution to $\mathbf{u}=A \mathbf{u}$, and $S$ is a constant, nonsingular matrix of the same size as $A$, then $\mathbf{v}(t)=S \mathbf{u}(t)$ solves the linear system $\mathbf{v}=B \mathbf{v}$, where $B=S A S^{-1}$ is similar to $A$.