Hello everyone,
After I run my model it gives an error " infeasible solution,reduced gradient less than tolerance" . where does this error come from? what I mean is,what can be done to prevent this problem?should I add any bounds?or the formulation has problem?
After I get this error,I dont know how should I fix it or which part of the model cause this problem
Thank you in advance for your help
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Hi again ! 
That error means that the solver has failed to find a feasible solution. You are right in your guesses, and everything can be happening. The problem can be wrongly formulated, appearing as mathematically infeasible, so check your formulation again.
If it is correctly written (and you know a feasible solution exists) then you need to “guide” the solver to this region by giving starting values to some variables (with x.l) and bounds.
In order to know if theres a certain part of the model that’s causing trouble, you can check the equation listing. There you can read which is the infeasibility at the starting point for each equation (INFES=…). This will guide you to which are the variables needing starting points or bounds. Also look for suspicious values in the variable listing (for example, variables having the same value when they should have opposite signs, point to a formulation sign error).
The more you know about the reality you’re trying to model, the easier it will be to “climb” out of infeasibility, so have in mind the “real” values variable can and should take.
regards
Claudio
On Sat, Apr 27, 2013 at 3:58 AM, Mohamad Dehghani wrote:
Hello everyone,
After I run my model it gives an error " infeasible solution,reduced gradient less than tolerance" . where does this error come from? what I mean is,what can be done to prevent this problem?should I add any bounds?or the formulation has problem?
After I get this error,I dont know how should I fix it or which part of the model cause this problem
Thank you in advance for your help
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ahan.,ok thank you very much
On Apr 29, 2013, at 10:40 PM, Claudio Delpino wrote:
Hi again !
That error means that the solver has failed to find a feasible solution. You are right in your guesses, and everything can be happening. The problem can be wrongly formulated, appearing as mathematically infeasible, so check your formulation again.
If it is correctly written (and you know a feasible solution exists) then you need to “guide” the solver to this region by giving starting values to some variables (with x.l) and bounds.
In order to know if theres a certain part of the model that’s causing trouble, you can check the equation listing. There you can read which is the infeasibility at the starting point for each equation (INFES=…). This will guide you to which are the variables needing starting points or bounds. Also look for suspicious values in the variable listing (for example, variables having the same value when they should have opposite signs, point to a formulation sign error).
The more you know about the reality you’re trying to model, the easier it will be to “climb” out of infeasibility, so have in mind the “real” values variable can and should take.
regards
Claudio
On Sat, Apr 27, 2013 at 3:58 AM, Mohamad Dehghani wrote:
Hello everyone,
After I run my model it gives an error " infeasible solution,reduced gradient less than tolerance" . where does this error come from? what I mean is,what can be done to prevent this problem?should I add any bounds?or the formulation has problem?
After I get this error,I dont know how should I fix it or which part of the model cause this problem
Thank you in advance for your help
--
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