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Manuscript Title: A Computer Program for Two-particle Generalized Coefficients of Fractional Parentage
Authors: A. Deveikis, A. Juodagalvis
Program title: GCFP, parGCFP
Catalogue identifier: AEBI_v1_0
Distribution format: tar.gz
Journal reference: Comput. Phys. Commun. 179(2008)607
Programming language: FORTRAN 77/90 (GCFP), C++ (parGCFP).
Computer: Any computer with suitable compilers. The program GCFP requires a FORTRAN 77/90 compiler. The auxiliary program parGCFP requires GNU-C++ compatible compiler, while its parallel version additionally requires MPI-1 standard libraries.
Operating system: Linux (Ubuntu, Scientific) (all programs), also checked on Windows XP (GCFP, serial version of parGCFP).
RAM: The memory demand depends on the computation and output mode. If this mode is not 4, the program GCFP demands the following amounts of memory on a computer with Linux operating system. It requires around 2 MB of RAM for the A = 12 system at Ex≤ 2. Computation of the A = 50 particle system requires around 60 MB of RAM at Ex = 0 and ~ 70 MB at Ex = 2 (note, however, that the calculation of this system will take a very long time). If the computation and output mode is set to 4, the memory demands by GCFP are significantly larger. Calculation of GCFPs of A = 12 system at Ex = 1 requires 145 MB. The program parGCFP requires additional 2.5 MB and 4.5 MB of memory for the serial and parallel version, respectively.
Keywords: Nuclear shell model, coefficients of fractional parentage, antisymmetric A-particle states, jt-coupling.
PACS: 03.65.-w, 02.70.-c, 03.65.Fd, 02.90.+p.
Classification: 17.18.

Nature of problem:
The code GCFP generates a list of two-particle coefficients of fractional parentage for several j-shells with isospin.

Solution method:
The method is based on the observation that multishell coefficients of fractional parentage can be expressed in terms of single-shell CFPs [1]. The latter are calculated using the algorithm [2,3] for a spectral decomposition of an antisymmetrization operator matrix Y . The coefficients of fractional parentage are those eigenvectors of the antisymmetrization operator matrix Y that correspond to unit eigenvalues. A computer code for these coefficients is available [4]. The program GCFP offers computation of two-particle multishell coefficients of fractional parentage. The program parGCFP allows a batch calculation using one input file. Sets of GCFPs are independent and can be calculated in parallel.

Restrictions:
A < 86 when Ex = 0 (due to the memory constraints); small numbers of particles allow significantly higher excitations, though the shell with j ≥ 11/2 cannot get full (it is the implementation contraint).

Unusual features:
Using the program GCFP it is possible to determine allowed particle configurations without the GCFP computation. The GCFPs can be calculated either for all particle configurations at once or for a specified particle configuration. The values of GCFPs can be printed out with a complete specification in either one file or with the parent and daughter configurations printed in separate files. The latter output mode requires additional time and RAM memory.
It is possible to restrict the (J, T) values of the considered particle configurations. (Here J is the total angular momentum and T is the total isospin of the system.) The program parGCFP produces several result files the number of which equals to the number of particle configurations. To work correctly, the program GCFP needs to be compiled to read parameters from the standard input (the default setting).

Running time:
It depends on the size of the problem. The minimum time is required, if the computation and output mode (CompMode) is not 4, but the resulting file is larger. A system with A = 12 particles at Ex = 0 (all 9411 GCFPs) took around 1 sec on a Pentium4 2.8GHz processor with 1 MB L2 cache. The program required about 14 mins to calculate all 1.3 × 106 GCFPs of Ex = 1. The time for all 5.5 × 107 GCFPs of Ex = 2 was about 53 hours. For this number of particles, the calculation time of both Ex = 0 and Ex = 1 with CompMode = 1 and 4 is nearly the same, when no other processes are running. The case of Ex = 2 could not be calculated with CompMode = 4, because the RAM memory was insufficient. In general, the latter CompMode requires a longer computation time, although the resulting files are smaller in size.
The program parGCFP puts virtually no time overhead. Its parallel version speeds-up the calculation. However, the results need to be collected from several files created for each configuration.

References:
[1] J. Levinsonas, Works of Lithuanian SSR Academy of Sciences 4 (1957) 17.
[2] A. Deveikis, A. Bonckus, R. Kalinauskas, Lithuanian Phys. J. 41 (2001) 3.
[3] A. Deveikis, R.K. Kalinauskas, B.R. Barrett, Ann. Phys. 296 (2002) 287.
[4] A. Deveikis, Comp. Phys. Comm. 173 (2005) 186. (CPC Catalogue ID. ADWI_v1_0)