For a given matrix $A$ we compute the matrix exponential $e^{tA}$
under the assumption that the eigenvalues of $A$
are known, but without determining the eigenvectors. The presented
approach exploits the connection between matrix exponentials and
confluent Vandermonde matrices $V$. This approach and the
resulting methods are very simple and can be regarded as an
alternative to the Jordan canonical form methods. The discussed
inversion algorithms for $V$ as well as the matrix representation
of $V^{-1}$ are of independent interest also in many other
applications.
Keywords:
Matrix exponential, Vandermonde matrix, Fast algorithm, Inverse