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Manuscript Title: Soliton bag model.
Authors: R. Horn, R. Goldflam, L. Wilets
Program title: BAG
Catalogue identifier: AALD_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 42(1986)105
Programming language: Fortran.
Computer: VAX 11/780.
Operating system: VAX/VMS.
RAM: 115K words
Word size: 32
Keywords: Particle physics, Elementary, Nonlinear, Differential equations, Soliton, Bag model, Phenomenological model.
Classification: 11.6.

Nature of problem:
The soliton bag model for QCD is a covariant field theory described by a complete Hamiltonian. The model is sufficiently general to describe either the MIT or SLAC bags by suitable limits of the parameters which determine the soliton field. Mathematically, the model consists of a nonlinear second order ordinary differential equation coupled with an eigenvalue problem for a coupled system of linear first order ordinary differential equations. The physical quantities calculated from the solutions of the differential equations are the rms charge radius, recoil corrected rms charge radius, bag energy, mean square momentum, recoil corrected bag mass, static magnetic moment, recoil corrected magnetic moment, and the axial-vector coupling constant.

Solution method:
The algorithm can be briefly described as follows:
Step 1: Choose an initial estimate for the soliton field.
Step 2: Using the current estimate for the soliton field, solve the eigenvalue problem, i.e. the Dirac wave function for the s1/2 state.
Step 3: Check for convergence of the soliton field, eigenvalue, and eigenfunctions. If the solutions have converged then proceed to step 5, otherwise continue to step 4.
Step 4: Using the current wave function, solve the nonlinear differential equation for the soliton field. The algorithm continues at step 2 using the new estimate of soliton field. Each completion of step 4 is called a cycle.
Step 5: If the number of constituents of the bag is three (i.e. a nucleon) and the recoil corrected rms charge radius exceeds .83 fm by some preassigned tolerance, then scale the length so that the recoil corrected rms charge radius .83 fm, scale the soliton field, eigenvalue, and the adjustable parameters so that the scaled soliton field and scaled eigenvalue is a solution of the mathematical model with scaled adjustable parameters and repeat starting at step 2. Otherwise continue to step 6. For measons no rescaling is done.
Step 6: Calculate the quantities of physical interest.

Running time:
34.54 seconds for the test case.