MGS
An Example of Legacy Code

MGS is intended to embody the problem of "legacy code", that is, software that is useful, but out of date, not documented, not well understood, and in need of some new features.

When approaching legacy software, it's useful to try to come up with good documentation for what the program is doing, a set of test problems which must be correctly handled by any new version of the software, and a set of timing problems that can show whether changes to the software have improved its efficiency.

In this case, the student is challenged to make a copy of the source code, read it, try to work out what it is doing, document it, and come up with a nice set of examples illustrating what is going on. A student might also be interested in the task of creating an equivalent version in a different language, and then demonstrating that the two programs produce the same results.

Languages:

MGS is available in a C version and a C++ version and a FORTRAN77 version and a FORTRAN90 version and a MATLAB version.

Author:

Diane O'Leary.

Reference:

1. Dianne O'Leary,
   Computational Software: Writing Your Legacy, Partial Solution to Last Issue's Homework Assignment,
   Computing in Science and Engineering,
   Volume 8, Number 2, March/April 2006, pages 70-71.

Source Code:

• mgs.m, the original version of the software.
• mgs_documented.m, a documented version of the software.
• mgs_fact.m, a revised version of the software.

Examples and Tests:

• mgs_test.m, a set of tests for MGS.
• mgs_test_output.txt, the results of running the test on MGS.
• mgs_timing.m, a set of timing tests for MGS.
• mgs_timing_output.txt, the results of running the timing test on MGS.
• mgs_timing.png, a PNG image of a graph of the timing of the MGS code versus the improved MGS_FACT version.

You can go up one level to the MATLAB source codes.