  In this paper, we review development of an algorithm that is referred to in
seismology as the Haskell matrix method, the Thomson-Haskell matrix method, or
the propagator matrix method. The roots of this algorithm and main developments
are examined to offer a better understanding of its essential features. The
underlying theory is highlighted by removing specific expressions and
manipulations that often shroud the common method involved. Also, I discuss
implementations of the algorithm in Python, with a reference to source code.
These implementations calculate dispersion curves for guided waves.
