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Manuscript Title: OLYMPUS restart facilities.
Authors: M.H. Hughes, K.V. Roberts
Program title: LEDGER
Catalogue identifier: ABUI_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 8(1974)123
Programming language: Fortran.
Computer: ICL SYSTEM 4/70.
Operating system: MULTIJOB.
RAM: 44K words
Word size: 8
Keywords: General purpose, Restart, Ledger, Utility.
Classification: 4.14.

Nature of problem:
Large scientific computer programs are often required to write periodic records to some output device so that a run may be stopped and restarted. The package described here provides general-purpose facilities for doing this, which are largely independent both of the program and also of the computer on which it is run.

Solution method:
Selected COMMON blocks of a Fortran program are wriiten to or read from a 'ledger file'. A library subroutine called LEDGER is provided, written in Standard Fortran, which performs various operations on this file. All the individual user has to do is to supply his own version of a simple ad hoc subroutine call ed RECORD which defines the blocks to be transmitted.

The package is intended primarily for use under the OLYMPUS system for initial-value Fortran programs, and communication is via labelled COMMON. Because Standard Fortran makes no provision for detecting end- of-file or error conditions, a non-standard READ statement has been used which is available on ICL and IBM computers. This however does not appear in LEDGER itself but only in two small subroutines RECORD and RECNUM which are easily changed, and we explain how to make the necessary changes for CDC computers as an example. The package also includes an assembler language subroutine UPDATE which obtains housekeeping information from the supervisor and must be recoded for a different type of computer system.