The check
conditions are evaluated each time that AMPL generates (or re-generates) an instance of your model. Normally the generation of an instance is triggered by a solve
command, but a few other commands such as write
and solution
can have the same effect.
You can force all check
statements to be evaluated immediately by typing the command
check;
or by inserting this command into an AMPL script at the point where you want the checking to occur.