It seems that the model that you are trying to solve is very difficult and/or very large. To get more information you should print the CPLEX status file by setting the following options:

• Solvers General option 'Solver window messages' to 'All';
• CPLEX option 'MIP display' to 'Nth node + info on node cuts'.

The CPLEX status file will be printed in the log folder. It would help if you could share the CPLEX status file.

can you please explain each step for the following work?

because I am unable to find it.

You can set options in the Option Tree, which can be opened by selecting Settings - Project Options in the menu bar. The attached screenshots show were you can find both options.

After setting both options you should solve your model again. The CPLEX status file will be named ‘CPLEX 12.8.sta’ and will be placed in the log folder in the project folder.

Hello @Marcel Hunting ,

Is the log of MIP display (“display each nth node) also can be generated using GUROBI solver?

Hi @rahmat , to print the Gurobi log you should set the Gurobi option 'Output File’ to 'Yes'.

Hi @Muhammad Furqan 

Were you able to get the log files after Marcel’s explanation? Or were you able to solve your issue yourself?

Best

Marcel,

attaced the log file and received cplex error again, after a long processing time. 

yes get the files. 

The CPLEX status file shows that CPLEX is running out of memory.

It seems that you are solving a Vehicle Routing Problem with Pickup and Delivery (VRPPD) or a Vehicle Routing Problem with Pick up and Delivery with Time Windows (VRPPDTW). Either problem seems to be very difficult to solve using an exact method and therefore in practice often heuristics are used to solve these problems. Sometimes also exact methods are used but they can be quite complex; see for example:

https://or.stackexchange.com/questions/2620/difficulties-with-finding-equivalent-problem-on-literature .

Formulating it as a MIP problem and solving it directly with a solver like CPLEX does not seem to be an efficient approach. Did you get your MIP formulation from a paper?

I am working on my thesis, but it becomes quite complex to solve the issue with the exact approach.

the error is occurring due to adding a timelimit constraint on each vehicle.