When I try to solve the attached model, I get the following errors:
Warning: The columns "TransportToCustomer(Warehouse1,Customer5,038.001,1)" and "TransportToCustomer(Warehouse1,Customer399,038.001,1)" are equal in the generated mathematical program "LeastCostPlan". This may lead to non-unique solutions. For more information regarding potential causes and consequences, see the help associated with the option "Warning_duplicate_column".
Warning: Only 3 out of 11565909 duplicate column warnings were reported. See also option limit_reported_duplicate_column_row_warnings.
Warning: After zero iterations CPLEX 12.7.1 concluded that an integer solution to LeastCostPlan does not exist.
Firstly, I don't really what this error means. In the example above, the shipping of product 038.001 to Customer5 on Period 1 and the shipping of product 038.001 to customer 399 on Period 1 do not have anything to do with each other, other than that they originate from the same warehouse and that it is the same product.
I have come across one similar problem in the old Google Groups community here:
There, it was mentioned that this may be due to the use of double variables. However, I don't think any of them are present in this model. Could there be any other reason that this is happening, and how could I go about solving this problem?
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