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Manuscript Title: COCHASE, a code for coupled channel Schrodinger equations.
Authors: S. Hirschi, E. Lomon, N. Spencer
Program title: COCHASE
Catalogue identifier: ABIC_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 9(1975)11
Programming language: Fortran.
Computer: IBM 360/65.
Operating system: OS 360 MFT/HASPII.
RAM: 122K words
Word size: 32
Keywords: Nuclear physics, S-matrix, Coupled channels, Phase shift, Inelasticity, Schrodinger equation, Coupled differential Equations, Runge-kutta, Newton-raphson, Direct reaction.
Classification: 17.11.

Nature of problem:
The computer code COCHASE is designed to calculate the S-matrix in the form of a real phase shift and inelasticity for the interaction of two particles coupled to the possible production of five other two particle channels. The production cross section for each secondary channel is also easily obtained.

Solution method:
The method of solution is to solve a set of coupled differential Schrodinger equations for the wave functions in each channel using a fourth order Runge-Kutta routine. Two simultaneous transcendental equations which involve these wave functions are then solved using the Newton-Raphson technique to find the phase shift and inelasticity.

The program is limited to the production of at most five two-particle channels. The potentials in the Schrodinger equations are assumed to be real and symmetric. Both of these restrictions are not essential and could be removed by some reprogramming. Those channels which involve Coulomb potentials are energy restricted, since numerical expressions have been used for the Coulomb functions which define the wave functions at large distances. These expressions hold for large rho (rho=kx). Since x is approximately 10 fermi and k is proportional to the energy, calculations below 10 MeV will be inaccurate. This restriction can be removed by using routines which have been written to calculate Coulomb functions in this region. There is also a problem with maintaining accuracy on the phase shift and inelasticity when far below inelastic thresholds. Double precision code is used for the test case.

Running time:
The test case which involved the production of two two-particle channels at four energies took 2 min of IBM 360/65 time to compile, link-edit and execute.