Adding TempConstr and an int

Answered

Valentin Guidon

April 11, 2023 17:35

• 
• 
• 

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

• 

  Valentin Guidon

  April 11, 2023 19:17

  • 
  • 
  • 

  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

   

  0

Please sign in to leave a comment.