Dear Cheikh Noufissa,

You find in this link the instances 

http://www.leandro-coelho.com/instances/inventory-routing/

http://mirplib.scl.gatech.edu/

http://www.optimization-online.org/DB_HTML/2013/08/4013.html

Dear Noufissa Cheikh,

Couples of major problems are observed during

· Relatively independent of the rest of the system.

· Direct shipping problems.

· Operational problem.

· In vehicle routing problems.

Solution;

Decompose a complex problem into a simpler problem, and produce sub-optimal solution.

Ashish