In a ``Classroom note'' published in Siam Review in 1996, I. E. Leonard revived Putzer's method on the basis that students who knew some differential equation theory could obtain a matrix exponential without being encumbered with any excessive knowledge of linear algebra - just eigenvalues and maybe the Cayley-Hamilton throrem.
The article produced a quick reaction whose results finally appeared in print two years later. The editor [25] introduced three new notes by commenting that the Note of Eduardo Liz [24] showed that one of Leonard's matrices was a Wronskian, the Note of M. Kwapisz uses Putzer's method to calculate the power of a matrix by exhibiting the power as the solution of a finite difference equation rather than Putzer's differential equation for the exponential, and Shui-Hung Hou's Note [22] was a reminder that the relation between traces and symmetric polynomials is a byproduct of the formula for the resolvent.