FORTRAN program for a numerical solution of the nonsinglet Altarelli-Parisi equation

Abstract

We investigate a numerical solution of the flavor-nonsinglet Altarelli-Parisi equation with next-to-leading-order $\alpha_s$ corrections by using Laguerre polynomials. Expanding a structure function (or a quark distribution) and a splitting function by the Laguerre polynomials, we reduce an integrodifferential equation to a summation of finite number of Laguerre coefficients. We provide a FORTRAN program for Q$^2$ evolution of nonsinglet structure functions (F$_1$, F$_2$, and F$_3$) and nonsinglet quark distributions. This is a very effective program with typical running time of a few seconds on SUN-IPX or on VAX-4000/500. Accurate evolution results are obtained by taking approximately twenty Laguerre polynomials.