variablesconstraintspyomofeasibility

Finding out reason of Pyomo model infeasibility

I got a pyomo concrete model with lots of variables and constraints.

Somehow, one of the variable inside my model violates one constraint, which makes my model infeasible:

WARNING: Loading a SolverResults object with a warning status into model=xxxx;
    message from solver=Model was proven to be infeasible.

Is there a way to ask the solver, the reason of the infeasibility?

So for example, lets assume I got a variable called x, and if I define following 2 constraints, model will be ofc. infeasible. 

const1:
    x >= 10

const2:
    x <= 5

And what I want to achieve that pointing out the constraints and variable which causes this infeasibility, so that I can fix it. Otherwise with my big model it is kinda hard to get what causing this infeasibility.

IN: write_some_comment
OUT: variable "x" cannot fulfill "const1" and "const2" at the same time.
Solution

  • Many solvers (including IPOPT) will hand you back the value of the variables at solver termination, even if the problem was found infeasible. At that point, you do have some options.

    There is contributed code in pyomo.util.infeasible that might help you out. https://github.com/Pyomo/pyomo/blob/master/pyomo/util/infeasible.py

    Usage:

    from pyomo.util.infeasible import log_infeasible_constraints
...
SolverFactory('your_solver').solve(model)
...
log_infeasible_constraints(model)