ObjBoundC not available

Answered

Gleb Belov

• October 14, 2020 02:18

Hi,

when solving a simple quadratic model, Gurobi finishes at root node. Then, trying to retrieve ObjBoundC, we get

Unable to retrieve attribute 'ObjBoundC'.
Failed to get the best bound. Gurobi error code: 10005

Is this expected behaviour and we should just take the primal value when dual bound not available?

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• 

  Jaromił Najman

  Gurobi Staff

  • October 14, 2020 07:24

  Hi Gleb,

  Could you post the simple quadratic model, such that we can try to reproduce this issue? If possible, please post a small self-contained code.
  
  Best regards,
  Jaromił

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• 

  Gleb Belov

  • October 15, 2020 00:23

  

  

  

  Hi Jaromił,

  the instance (recognized as convex quadratic, despite the equality) is this:

  Maximize
  obj
  Subject To
  p_times_0: - obj + [ x ^2 ] = 0
  Bounds
  x <= 10
  obj <= 100
  End

  When I call gurobi_cl ResultFile=result.json instance.lp, the json result file contains

  { "SolutionInfo": { "Status": 2, "Runtime": "3.2305717468261719e-04", "ObjVal": "100", "BoundVio": "0", "ConstrVio": "0", "IterCount": "0", "BarIterCount": 0}}

  i.e., ObjBound(C) are not there. For a slightly more complicated instance, which is also solved at root but at least requires 1 iteration of barrier, the bounds are there. I am happy to write C code but I think this shows the issue (if it is not the intended behaviour, but the documentation says nothing except that the attributes are intended for MIPs).

  Cheers, Gleb

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• 

  Silke Horn

  Gurobi Staff

  • October 15, 2020 07:23

  Hi Gleb,

  Thanks for posting the example. The ObjBoundC attribute is not available since your model is not a MIP. If you change the type of one of your variables to integer, Gurobi will compute the ObjBoundC.

  Best regards
  Silke

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