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1.6 Data Structures

The modules communicate with each other via standardized Data Structures (DS). They are processed in blocks by utility subroutines to ensure simple manipulation. A DS may reside:

in main memory,

in the form of a set of dynamic arrays,

in secondary memory,

in the form of a file (an unformatted Fortran file consisting of several records).

Amongst the numerous advantages of Data Structures, let us note the following:

• The interfaces between modules are standardized, simple and reliable.
• The number of parameters per module is reduced. In fact, a DS reorganizes a large amount of information, as for example the complete mesh definition.
• The programming of modules is facilitated by predefined reading, writing and printing tools.

All Data Structures have a type, for example NOPO, MAIL, COOR, or B. The different arrays belonging to a DS of a given type are described in part iii of this user guide. If a DS is of a generic type, tysd, it can be manipulated in a module via the following variables:

CHARACTER*80 NOMFIC

:
The file name (see [Fortran 77], command: OPEN, specifier: FILE).

INTEGER NFtysd

:
The file unit number (see [Fortran 77], command: OPEN, specifier: UNIT). NFtysd = 0 signifies that the DS is in main memory.

INTEGER NItysd

:
An integer, called the level, which enables us to distinguish between two Data Structures of the same type, residing in main memory at the same time.

Remarks:

• Experience has shown that the Fortran command, OPEN, is not totally portable. Consequently, this instruction is not allowed in MODULEF and utility OUVRIR (p. ) or OUVRIS (p. ) is called instead.
• Programs manipulating files often require a free unit number, i.e. not assigned to any other file. Utility, TRUNIT (p. ) is used to obtain such a number.

To conclude, the calling of a module which requires, for example, a NOPO type DS typically has the following form:

      ...
      CALL TRUNIT(NFNOPO)
      NINOPO = 0
      CALL LIBCAR(NOMFIC)
      CALL OUVRIS(NFNOPO, NOMFIC, 'OLD,UNFORMATTED', 0)
      CALL MODULE(M, NFNOPO, NINOPO, ...)
      ...