“…This function was called the Evans function by Alexander, Gardner and Jones [2], who generalized its definition considerably. Since then, the Evans function has been used frequently for stability analysis; see, for example, [1,3,4,6,15] for numerical computations employing the Evans function and [11,22,30,34,35] for an analytic treatment. The review paper by Sandstede [33] gives an excellent overview of the field.…”