Adding TempConstr and an int

Answered

Valentin Guidon

April 11, 2023 17:35

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Hello, I want to minimize the number of tasks that start at the same time. Here is my attempt with 2 tasks which can start at any day between day 0 and day 4.

 

from gurobipy import *

# Create a new model
m = gp.Model("very simple LP")

# Create variables
T1 = m.addVar(vtype=gp.GRB.INTEGER)
T2 = m.addVar(vtype=gp.GRB.INTEGER)
requests = [T1,T2]
nb_days = 10
nb_requests= 2

# Set objective
m.setObjective( quicksum( [(r ==i ) for r in requests for i in range(nb_days)] )
                         , sense= gp.GRB.MINIMIZE)

# Add constraints:
m.addConstr( 1 <= T1 )
m.addConstr( T1 <= 4 )
m.addConstr( 1<= T2  )
m.addConstr( T2 <= 4 )
# Optimize model
m.optimize()

But if I'm launching this program, I have 

unsupported operand type(s) for +=: 'gurobipy.LinExpr' and 'TempConstr'

How can I proceed to remove this error ?

Thanks in advance !!

Related to

• Syntax Error

0

• Official comment

  

  Simranjit Kaur

  • Gurobi Staff

  November 13, 2026 01:45

  This post is more than two years old. Some information may not be up to date. For current information, please check the Gurobi Documentation or Knowledge Base. If you need more help, please create a new post in the community forum, or try Gurobot, our chatbot interface offering instant, expert-level support.
• 

  Valentin Guidon

  April 11, 2023 19:17

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  Hey, I've rewritten my code to make it more readable and understand exactly where I'm blocking

  from gurobipy import *

  # Create a new model
  m = gp.Model("task_scheduling")

  # Create variables
  T1 = m.addVar(lb=1, ub=4, vtype=gp.GRB.INTEGER, name='T1_start_time')
  T2 = m.addVar(lb=1, ub=4, vtype=gp.GRB.INTEGER, name='T2_start_time')
  requests = [T1, T2]
  nb_days = 5
  nb_requests = 2

  #For each day i and each task j, x[i, j] represent whether that task starts on that day
  x = m.addVars(range(nb_days), range(nb_requests), vtype=gp.GRB.BINARY, name=f'x')

  
  # Set objective: minimize the total number of tasks that start on each day.
  m.setObjective(quicksum(x.sum(i) for i in range(nb_days)), sense=gp.GRB.MINIMIZE)

  
  # Add constraints:

  for i in range(nb_days):
      for j in range(nb_requests):
          if requests[j] == i:
              x[i,j]= 1
          else: 
              x[i,j]= 0
  # Optimize model
  m.optimize()

  # Print results
  #print(f'Minimum number of tasks starting on the same day: {m.objVal}')
  #print(f'Task T1 starts on day {int(T1.x)}')
  #print(f'Task T2 starts on day {int(T2.x)}')
  #for v in m.getVars():
  #    print('%s %g' % (v.varName, v.x))

  I can't write in "gurobi language" the text in bold 

  0
• 

  Matthias Miltenberger

  • Gurobi Staff

  April 12, 2023 17:12

  Hi Valentin,

  You can use indicator constraints to model such relationships. Please have a look at this guide for further information: How do I model conditional statements in Gurobi?

  Cheers,
  Matthias

   

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