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

We investigate a numerical solution of the flavor-nonsinglet Altarelli-Parisi equation with next-to-leading-order α 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 non-singlet 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. Programming language used: FORTRAN 77 Peripherals used: laser printer No. of lines in distributed program, including test data, etc.: 1111 Nature of physical problem This program solves the Altarelli-Parisi equation for a spin-independent flavor-nonsinglet structure function or quark distribution. Method of solution We expand an initial quark distribution (or a structure function) and a splitting function by Laguerre polynomials. Then, the solution of the Altarelli-Parisi equation is expressed in terms of the Laguerre expansion coefficients and the Laguerre polynomi-als. Restrictions of the program This program is used for calculating Q 2 evolution of a spin-independent flavor-nonsinglet structure function or quark distribution in the leading order or in the next-to-leading-order of α s. The double precision arithmetic is used. The renormalization scheme is the modified minimal subtraction scheme (MS). A user provides the initial structure function or the quark distribution as a subroutine. Examples are explained in sections 3.2, 4.13, and 4.14. Then, the user inputs thirteen parameters explained in section 3.1. Typical running time Approximately five (three) seconds on SUN-IPX (VAX-4000/500) if the initial distribution is provided in the form of a 1 x b 1 (1 − x) c 1 + a 2 x b 2 (1 − x) c 2 + · · · in the subroutine GETFQN. If Laguerre coefficients of the initial distribution in the subroutine FQNS(x) are calculated by a GAUSS quadrature, the running time becomes longer depending on the function form.