A semianalytical method to evolve parton distributions

We present a new method to solve in a semianalytical way the Dokshitzer-Gri bov-Lipatov-Altarelli-Parisi evolution equations at NLO order in the x-spac e. The method allows to construct an evolution operator expressed in form o f a rapidly convergent series of matrices, depending only on the splitting functions. This operator, acting on a generic initial distribution, provide s a very accurate solution in a short computer time (only a few hundredth o f second). As an example, we apply the method, useful to solve a wide class of systems of integrodifferential equations, to the polarized parton distr ibutions. (C) 1999 Published by Elsevier Science B.V, All rights reserved.