Error: ufunc 'subtract' cannot use operands with types dtype('<M8[ns]') and dtype('O')

Answered

Ru Xin Chua

March 08, 2022 05:27

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I encountered this error while trying to solve a VRP. I am not very sure how to convert the date time and gurobi var such that they can subtract each other

https://stackoverflow.com/questions/71385265/error-numpy-core-exceptions-ufuncbinaryresolutionerror-ufunc-subtract-cann 

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  Ru Xin Chua

  March 08, 2022 10:42

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  variable t is tupledict while arrivaltime is timedate64. that is why subtraction not possible. any idea how to convert

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  Jaromił Najman

  • Gurobi Staff

  March 08, 2022 11:13

  Could you please generate a minimal reproducible example showing the issue? Currently, it is not possible to execute your code, because all data is missing.

  Other than that, it does not seem to be a Gurobi issue but rather a data type issue. You should try to track down which subtraction exactly is responsible for the error.

  Best regards, 
  Jaromił

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  Ru Xin Chua

  March 08, 2022 12:54 Edited

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  This variable gives a datatype of datetime64[ns]

  arrival=np.array(data["Vessel Arrival Time"])

   

  This variable gives a datatype of gurobi.var

  t=model.addVars(vessel_number,vtype=GRB.CONTINUOUS ,name="t")

   

  I get this when I check the first index of t

  t[0]

   

   

  <gurobi.Var *Awaiting Model Update*>

  <gurobi.Var *Awaiting Model Update*>

   

  The subtraction that caused the error is 

  constraint5=model.addConstrs(w[i]>=arrival[i]-t[i]for i in range(vessel_number) )

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  Jaromił Najman

  • Gurobi Staff

  March 08, 2022 13:24

  The error occurs because it is not possible to subtract/add Gurobi optimization variables from/to a datetime64[ns] object. You have to somehow convert your arrival values to numerical values. This stackoverflow thread should be helpful.

  Best regards, 
  Jaromił

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