Bad suffix .iis when problem is not infeasible.

[nhh1...@gmail.com]

Hi! I am trying to run an analysis when problems are infeasible. Hence, I have defined `iisfind=1` in the CPLEX options and this code block to ensure the results of the infeasibility analysis is saved to file only if infeasibility exists:

if solve_result_num >= 200 and solve_result_num < 300 then {

  display _varname, _var.iis > out/infeasibility_analysis_variables.txt;

  display _conname, _con.iis > out/infeasibility_analysis_constraints.txt;

}

When infeasibility do exist, this solution works perfectly. However, I get an error message when the problem is feasible and, for instance, stopped because of a time liimit. Which I find strange because the code to write these files are wrapped by an if statement that should not be run for feasible problems.

run.txt, line 54 (offset 2346):

Bad suffix .iis for _con

context:  display _conname,  >>> _con.iis  <<< > out/infeasibility_analysis_constraints.txt;

Possible suffix values for _con.suffix:

astatus   body      defvar   derstage

dinit     dinit0    dual     lb

lbs       lbs1      lbs2     ldual

lslack    no        relax    slack

sno       sstatus   stage    status

ub        ubs       ubs1     ubs2

udual     uslack 

Does anyone have a suggestion on how to solve this issue? I prefer not to add the `iis` settings only if problems become infeasible as that is not a sufficiently automatic approach for me.

Thank you in advance!

Best,

Christian

[nhh1...@gmail.com]

I found the answer here: https://groups.google.com/g/ampl/c/z1CwzJv0FWU

The problem was that the suffix does not exist, as the error message correctly stated. Hence, the suffic must be defined first with:

suffix iis symbolic OUT;

Best,

Christian