A Small Update to simann.f90
October 2, 2013
Thomas Ruedas wrote to me some time ago regarding a typo in simann.f90, the simulated annealing module contained in the archive of Alan Miller’s Fortran Software that I host:
exprep, the condition of the second IF branch reads:
ELSE IF (rdum < -180.+dp) THEN
whereas the correct form should be
ELSE IF (rdum < -180._dp) THEN
180as double precision (
_dp), as defined earlier in the code. That would also correspond to the original (single prec.) formulation and, for instance, the first
IF (rdum > 174._dp) THEN
The bug does not result in a compilation error, and does probably not affect the test case, at least not on my machine, but it may nonetheless lead to a wrong result in some circumstances.
My response to Dr. Ruedas was:
In the case you report, I agree with you that it’s clearly a bug. When I run Alan’s
TO_F90on the original Fortran 77 program, the
_dpspecifiers are not there, so he likely added them by hand. Of course, plus (
+) is very close on the keyboard to the underscore (
_), and both require pressing shift. There’s no compiler error unless you have type conversion warnings turned on, so it went unnoticed.
As I’ve mentioned previously, I have no plans to actively maintain Alan’s collection of algorithms. Even if I had time to do so, many of them fall outside my realm of expertise, so it would be imprudent of me to attempt to do so. However, in this case I am familiar with simulated annealing and this seems to be a clear typo, so I have updated the hosted version of simann.f90 accordingly. For reference, the previous last modified date on that file was August 3, 1997.