I always thought of the general preliminary for a graduate program in applied math as Calculus, Real analysis, Complex variables, DE, introductory Linear algebra, probability and statistics etc. But I read somewhere undergrads looking into graduate degrees in applied math should also take a course in discrete mathematics, and theory of equations, is this necessary?
Note: This is not so much a requirement as building up a strong background for research to come. I guess in this sense, I am asking how discrete mathematics and equation theory relate to applied math.