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I have some questions about the three asterisks (***) in GAMS that may be shown at the end of an individual equation listing. I know they are a warning that the constraint is infeasible at the starting point. I have a model that after solving it by GAMS, the model status and solver status are ‘1’ and the equation seems to be feasible, but at the end of an equation three asterisks are shown.

I want to know:

1) What is the starting point?

2) Is the model infeasible?

I really appreciate your kind helps.

saeed
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1 Answers1

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The starting point (or initial point) is comprised of the values of the decision variables just before the solver starts optimizing them. You can change the initial values by assigning say x.l(i) = 5. Note that the default in GAMS is zero (but may be projected to the closest bound just before the solve: variables will always between their bounds in the initial point).

These *** mean that the initial value is such that some equations are not feasible. In general this is not something to worry about. The solver will try to return a feasible and optimal point even if the initial point is not feasible. Sometimes we want to make sure the initial point is feasible for performance reasons, and then this part of the listing file can be a useful debugging tool.

Note that an infeasible initial point does not say anything about whether the model is infeasible.

Erwin Kalvelagen
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  • you are right. I read about that, but I did not found my exact answer. now I realize that the model is feasible. Thank you very much. It was very helpful. – saeed Oct 09 '16 at 19:27