Originally posted by: story_

Hi,

I am working on an LP problem, where I am trying to determine the infeasible constraints for a given solution. Once I feed the solution into the problem, I receive the following message in the engine log:

Tried aggregator 1 time.
LP Presolve eliminated 108 rows and 49 columns.
Aggregator did 17 substitutions.
Reduced LP has 21 rows, 35 columns, and 92 nonzeros.
Presolve time = 0.00 sec. (0.07 ticks)
Initializing dual steep norms . . .

Iteration log . . .
Iteration:     1   Dual objective     =          4045.095000
Iteration:    25   Dual objective     =          4045.095000

Iteration log . . .
Iteration:     1   Dual objective     =             0.000000
Iteration:    62   Dual objective     =           153.715871

I have solved the same LP for other solutions, and the engine log indicated the specific rows that were infeasible in those cases. I was wondering under what circumstances the infeasible row isn't mentioned and how I could find the constraint(s) that violate the solution.

Thank you.

You will see this output of infeasible rows only if the model is blatantly infeasible. If the infeasibility is more subtle or involves more than one row then you will have to run the conflict refiner to find a minimal set of conflicting rows and bound constraints. If you label your constraints in the model then the conflict refiner should automatically be run on infeasible models.