GurobiError "Constraint has no bool value" is fixed by flipping the constraint.

Answered

Hussein Sharadga

December 04, 2022 00:55 Edited

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In the following code: x is constant, and B is the optimization variable. I have the following constraint.
\[x<=sum(B)\]
This constraint is the source of the problem.

If I flip it as follows, the problem is solved:

\[sum(B)>=x\]

If you go to the for loop, I comment out the first formulation. The first formulation produces the error. I am just curious why the first formulation is not working. 

import numpy as np
m=gp.Model()
cost=[-70,-60,-50,-40,-30,-20,-10,0]
cost=np.flipud(cost)
x=[1,0,0,1,1,1,0,0]
x=np.flipud(x)



B=m.addVars(len(x), vtype=GRB.BINARY)
obj=gp.quicksum(cost[i]*B[i] for i in range (len(x)))
m.setObjective(obj)

m.addConstr(gp.quicksum(B[i] for i in range (len(x)))<=1 )
m.addConstrs(B[i]<=x[i] for i in range (len(x)))

for i in range(len(x)): 
    
    #m.addConstr(x[i]<=gp.quicksum(B[jj] for jj in range (i+1)))
    m.addConstr(gp.quicksum(B[jj] for jj in range (i+1))>=x[i])
    
m.optimize() 
    

 

Thanks,

Hussein

Related to

• Formulation
• Syntax Error

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  Jaromił Najman

  • Gurobi Staff

  December 05, 2022 09:32

  Hi Hussein,

  This issue is discussed in the second paragraph of Constraint has no bool value (are you trying "lb <= expr <= ub"?).

  A workaround is

  m.addConstr(int(x[i]) <= gp.quicksum(B[jj] for jj in range (i+1)))

  Best regards, 
  Jaromił

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  Hussein Sharadga

  December 06, 2022 03:26 Edited

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  Thank you so much! Jaromił Najman

   

   

  Best,

  Hussein

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