With respect to error messages it has been decided to use the so-called "hard"
option, which means that immediately after an error an error message will be given
and if necessary the program is halted.
The soft option, which means returning with an error number in the parameter
list is only applied if a numerical method produced an error, for example
because no convergence appeared.
It is advised to use a standard subroutine that produces the error messages
and also delivers a trace back if possible. This subroutine should be such
that an error message is clearly visible in the output file
by producing sufficient blank lines
and a clear indicator. An alternative is to write the error messages to a
separate file. However, experience learns that user are not inclined to
read this file and as a consequence errors might not be noted. For that
reason it is advised to write errors to the standard output file.
There must be a clear distinction between errors and warnings. If too much
errors have been produced, stop the program, if there are too much warnings,
suppress subsequent warnings.
In SEPRAN all errors must be given by the error subroutine ERRSUB and all
warnings by ERRWAR.
In ISNaS the error subroutine is called ISERRSUB and the warning subroutine
ISWARSUB. These subroutines have already been adapted for a parallel environment.