QUALITY CONTROL -- Documentation of computer programs used for aquifer modeling

                        GEOLOGICAL SURVEY
                        RESTON VIRGINIA  22092

                                                  Code 4351 5016

                                             February 26, 1979


SUBJECT:  QUALITY CONTROL -- Documentation of computer programs
                             used for aquifer modeling

Significant modifications to existing models or newly devised
computer programs used to simulate aquifer processes should be
documented before the programs or interpretations based on them
are released.  This memorandum amplifies earlier instructions
regarding the need to document modifications of existing computer
programs, and provides guidelines for documentation of new
computer programs.

Ground Water Branch Technical Memorandum No. 75.11 (a copy is
attached) provided guidelines for reporting and documenting
aquifer modeling analyses.  Item #7 of that memo indicated, among
other things, that if the computer program used is "substantially
different" from a published version, the "significant
modifications" of the original program should be described in an
open file or published report.  A "significant modification" to a
computer program means any change in the computational scheme that
can give computed results that may differ from those that would be
obtained using the published version of the program.  Changes in
format of data input and/or output are not considered significant.
However, changes in the approximating equations and/or the
algorithm used to solve those equations are considered
significant.  If the description of those modifications is
extensive or is believed to disrupt the continuity of the report,
those modifications can be described in an appendix to the report.

A newly developed program, representing a computational approach
that is different from published approaches, should be documented
in a report released prior to, or as a part of, the report giving
results of a hydrologic analysis using that program.  The
documentation should precede, or be coincident with, release of
copies of the computer program for use outside of the Geological
Survey.  The "documentation" of newly developed programs and major
program modifications should include at a minimum a description of
the computational procedure in sufficient detail to provide enough
information to independently develop an equivalent computer
program.  However, if a newly developed program is intended for
widespread use in the U.S. Geological Survey, it would be
preferable for the documentation to include a generalized flow
chart, program listing, definitions of program variable,
instructions for the preparation of the data input, and a sample
of the output.  These requirements are intended to assure that
adequate information on computer programs used to make hydrologic
analyses is released in a timely fashion.

                                   (s) Gerald Meyer
                                   Chief, Ground Water Branch


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