Topic
  • 3 replies
  • Latest Post - ‏2013-02-12T21:49:46Z by SystemAdmin
SystemAdmin
SystemAdmin
7929 Posts

Pinned topic Cplex Net optimizer | arc solution = 1 with upper bound = 0

‏2013-02-06T12:02:23Z |
Hi

I am using Cplex net optimizer (C). I set some upper bounds of the arcs to zero using "CPXNETchgbds" but
when cplex solve the net it still uses any of them. It this possible?

Cplex should take another arc but it takes the same one over and over.

Thank you for your time
Updated on 2013-02-12T21:49:46Z at 2013-02-12T21:49:46Z by SystemAdmin
  • SystemAdmin
    SystemAdmin
    7929 Posts

    Re: Cplex Net optimizer | arc solution = 1 with upper bound = 0

    ‏2013-02-10T10:13:31Z  
    That should clearly not happen. How big is the flow on the arc with upper bound 0? May it be that it is very small and you are just suffering from numerical round-off?
    Could you also export the network using CPXNETwriteprob and double check that the bounds on the arcs are as expected?
  • SystemAdmin
    SystemAdmin
    7929 Posts

    Re: Cplex Net optimizer | arc solution = 1 with upper bound = 0

    ‏2013-02-12T11:15:18Z  
    That should clearly not happen. How big is the flow on the arc with upper bound 0? May it be that it is very small and you are just suffering from numerical round-off?
    Could you also export the network using CPXNETwriteprob and double check that the bounds on the arcs are as expected?
    Thanks for your answer,
    I've exported the model to a .lp file: (BOUNDS)
    http://...
    0 <= x63 <= 1
    0 <= x64 <= 1
    x65 = 0
    x66 = 0 <----- (I'm using default arc names so x66 corresponds to arc 65 in the model)
    0 <= x67 <= 1
    0 <= x68 <= 1
    http://...

    Cplex's solutions:
    http://....
    Arc 63: Value = 0.000000 Reduced cost = 403.975342
    Arc 64: Value = 0.000000 Reduced cost = -1.036865
    Arc 65: Value = 1.000000 Reduced cost = 603.963074 <-----
    Arc 66: Value = 0.000000 Reduced cost = 0.000000
    Arc 67: Value = 0.000000 Reduced cost = 604.999939
    http://...

    How I can know the flow on the arc? I'm looking up for a function in the callable library but I haven't found anything yet.
    Sorry if it's sounds very basic, I'm new in Cplex

    Thank you
  • SystemAdmin
    SystemAdmin
    7929 Posts

    Re: Cplex Net optimizer | arc solution = 1 with upper bound = 0

    ‏2013-02-12T21:49:46Z  
    Thanks for your answer,
    I've exported the model to a .lp file: (BOUNDS)
    http://...
    0 <= x63 <= 1
    0 <= x64 <= 1
    x65 = 0
    x66 = 0 <----- (I'm using default arc names so x66 corresponds to arc 65 in the model)
    0 <= x67 <= 1
    0 <= x68 <= 1
    http://...

    Cplex's solutions:
    http://....
    Arc 63: Value = 0.000000 Reduced cost = 403.975342
    Arc 64: Value = 0.000000 Reduced cost = -1.036865
    Arc 65: Value = 1.000000 Reduced cost = 603.963074 <-----
    Arc 66: Value = 0.000000 Reduced cost = 0.000000
    Arc 67: Value = 0.000000 Reduced cost = 604.999939
    http://...

    How I can know the flow on the arc? I'm looking up for a function in the callable library but I haven't found anything yet.
    Sorry if it's sounds very basic, I'm new in Cplex

    Thank you
    Finally I've found the problem

    It was my fault, solution status was infeasible and cplex was returning the last feasible solution. I'm working in a problem
    which has hundreds of nets and this net had an issue :( .

    Thanks for your help