J3/04-251

To:          J3
From:        Craig Dedo
Date:        February 16, 2004
Subject:     Greater Than 7 Array Dimensions

Number:

Title:                Greater Than 7 Array Dimensions

Submitted By:    Craig Dedo

Status:            For Consideration

References:


Basic Functionality:
    The next Fortran standard should have a maximum limit on the number
of array dimensions of greater than 7.  Processors should be able to
support more than the new maximum as an extension.

Rationale:
    The original limit of 7 dimensions in Fortran was established when
the first Fortran standard was published in 1966 and has never been
changed since.  The number of heavy duty applications which require more
than 7 dimensions is growing and becoming a significant proportion of
high performance applications.  Since Fortran does not now support more
than 7 dimensions, programmers of an application which requires more
than 7 dimensions usually write their application in another language.
They do this even though in most cases they are more familiar with
Fortran and would prefer to use Fortran.

Estimated Impact:
    There would be no impact on existing codes.  It should be fairly
easy to write the specification in the standard.  A few Fortran
processors and some processors in other languages already support more
than 7 array dimensions, so the technology of implementing high limits
on array dimensions is well understood.  Implementors most likely will
need to modify their descriptors and symbol tables in order to support
the larger limit.

Detailed Specification:
    The constraint limiting the number of array dimensions would need to
be raised to a higher limit.
    We would need to develop a syntax that would allow a programmer to
specify subranges of dimensions.  Research into human psychology
indicates that short-term memory is limited to around 7 items, so it
would be useful to give the programmer a way of avoiding the need to
count large numbers of dimensions.

History: