In this paper, a general method is presented that allows the derivatio
n of the expansion coefficients of the product of two orthogonal funct
ions provided the generating function is known. For the three classica
l orthogonal polynomials, the Laguerre, the Hermite, and the Legendre
polynomials, the coefficients b(lmn) with phi(m)phi(n) = SIGMA(l)b(lmn
)phi(l) are derived. (C) 1993 John Wiley & Sons, Inc.