RS01221: CPLEX CAN CLAIM OPTIMALITY ON AN INFEASIBLE NETWORK WITH A SUPPLY/DEMAND IMBALANCE AND NEGATIVE FLOW AT THE ROOT NODE

APAR status

• Closed as fixed if next.

Error description

• If a network has a supply/demand imbalance that forces flow
  into the root node (i.e. the first node specified in the input),
  CPLEX will declare optimality even though the solution is
  obviously infeasible.  For example, the network
  
  MINIMIZE NETWORK netex1
  SUPPLY
  n1 : 1
  n4 : -5
  ARCS
  a1 : n1 -> n4
  OBJECTIVE
  a1 : 3
  BOUNDS
   0 <= a1 <= 25
  ENDNETWORK
  
  
  Results in
  
  CPLEX> r bad.net
  Problem 'bad.net' read.
  Read time =    0.00 sec.
  CPLEX> net
  Iteration log . . .
  Iteration:     0   Infeasibility     =             5.000000 (5)
  
  Network - Optimal:  Objective =  1.5000000000e+01
  Solution time =    0.00 sec.  Iterations = 1 (1)
  
  This exists for versions 10.0 - 12.5.   It has been fixed
  in 12.5.0.1.
  
  No workaround available.   This will typically only happen
  on tiny networks like the one above where there is no
  flexibility regarding the flows resulting from the imbalance.
  
  Keeping call open for now until additional info regarding the
  network configurations that cause this bug to bite is available.
  

Local fix

• No workaround available; see problem description for more
  details.
  

Problem summary

•  Some networks with obvious supply/demand imbalances may result
  in an incorrect claim of optimality.
  

Problem conclusion

Temporary fix

• No.
  

Comments

APAR Information

• APAR is sysrouted FROM one or more of the following:

• APAR is sysrouted TO one or more of the following:

Fix information

Applicable component levels

• RC50 PSY

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