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How can I get constraints to find the maximum completion time in each machines?

Ongoing
Jirayu Bamroongwongsiri
Gurobi-versary
First Comment
First Question

I have tried to create the constraints to get the max value of completion time for each machine.

import gurobipy as gp
from gurobipy import GRB

import pandas as pd
m = gp.Model("Sustainable")
Num_of_machines = 3
Machines = range(1,Num_of_machines+1)

Num_of_jobs = 9
Jobs = range (1,Num_of_jobs+1)

Time_span = 24
Times = range(1,Time_span+1)

Times_buffer = range(1,Time_span+10)

Processing = {1:4,2:2,3:3,4:1,5:1,6:5,7:3,8:3,9:5}

Due_date = {1:4,2:3,3:4,4:2,5:6,6:8,7:10,8:11,9:7}
x = {}
for i in Jobs:
    for j in Machines:
        for k in Times_buffer:
            x[i,j,k] = m.addVar(vtype = GRB.BINARY,name = "x")           
y = {}
for j in Machines:
    for k in Times:
        y[j,k] = m.addVar(vtype = GRB.BINARY,name = "y")
        
s = {}
for i in Jobs:
    for j in Machines:
        for k in Times:
            s[i,j,k] = m.addVar(vtype = GRB.BINARY,name = "s")
Starting_buffer_const = m.addConstrs(((gp.quicksum(gp.quicksum(s[i,j,k]* Times[Times.index(k)] for j in Machines) for k in Times)) <= Time_span - Processing[i] for i in Jobs), name = "Starting_buffer_const")

Starting_time_Consts = m.addConstrs((gp.quicksum(gp.quicksum(s[i,j,k] for j in Machines) for k in Times) == 1 for i in Jobs) , name = "Starting_Const")

machine_status = m.addConstrs((gp.quicksum(x[i,j,k] for i in Jobs) + y[j,k] == 1 for j in Machines for k in Times),name = "Machine_status")

Machine_capacity = m.addConstrs((gp.quicksum(x[i,j,k] for i in Jobs) <= 1 for j in Machines for k in Times), name = "Machine_capacity")

Production_Const = m.addConstrs(((gp.quicksum(x[i,j,k] for k in range(k,k+(Processing[i]))) >= s[i,j,k]*Processing[i]) for i in Jobs for j in Machines for k in Times),name = "Production_const")

aux1 = m.addVars(Jobs, lb = -20.0, vtype=GRB.CONTINUOUS, name="aux1")
aux2 = m.addVars(Jobs, lb = -20.0, vtype=GRB.CONTINUOUS, name="aux2")
Max_Completion_Time = m.addVars(Jobs, lb = -0.0, vtype=GRB.CONTINUOUS, name="Max_Completion_Time")

Earliness_i = m.addVars(Jobs, vtype=GRB.CONTINUOUS, name="Earliness")
Tardiness_i = m.addVars(Jobs, vtype=GRB.CONTINUOUS, name="Tardiness")

completion_time = {}
for i in Jobs:
    for j in Machines:
        completion_time[i, j] = m.addVar(vtype=GRB.CONTINUOUS, lb=0, name="completion_time")
        
Starting_job = {}
for i in Jobs:
    Starting_job[i] = (gp.quicksum(gp.quicksum(s[i,j,k] for j in Machines)*k for k in Times))
    completion_time[i,j] = Starting_job[i]+Processing[i]

max_completion_time = {}
for j in Machines:
    max_completion_time[j] = m.addGenConstrMax(Max_Completion_Time[j],completion_time[i, j],name="Max_completion_time")
            
Tardy = m.addConstrs((Starting_job[i] + Processing[i] - 1 - Due_date[i] - aux1[i] == 0 for i in Jobs), name="aux_constr1.1")
Early = m.addConstrs((Due_date[i] - Starting_job[i] - Processing[i] + 1 - aux2[i] == 0 for i in Jobs), name="aux_constr1.2")

Tardy_Cal = m.addConstrs((Tardiness_i[i] == gp.max_([aux1[i], 0.0]) for i in Jobs), name="aux_constr2.1")
Early_Cal = m.addConstrs((Tardiness_i[i] == gp.max_([aux1[i], 0.0]) for i in Jobs), name="aux_constr2.2")

It got an error here "TypeError: object of type 'Var' has no len()". How can I fix this problem?

Thank you

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Comments

7 comments

Date Votes
  • Simranjit Kaur
    Gurobi Staff Gurobi Staff
    • Edited

    Hi,

    To find the maximum completion time for each machine, you can use the following code:

    Max_Completion_Time = m.addVars(Machines, vtype=GRB.CONTINUOUS, name="Max_Completion_Time")
    completion_time     = m.addVars(Jobs, Machines,vtype=GRB.CONTINUOUS, lb=0, name="completion_time")

    Max_Completion_Time_constrs = m.addConstrs( (Max_Completion_Time[j] == gp.max_(completion_time[i, j] for i in Jobs) for j in Machines), name= "Max_Completion_Time")
    Also, note that with your following code, all x variables get the same name, "x"
    for i in Jobs:
    for j in Machines:
        for k in Times_buffer:
            x[i,j,k] = m.addVar(vtype = GRB.BINARY,name = "x")
    You can use the addVars() method to ensure your variables get names based on indices.
    x = m.addVars( Jobs, Machines, Times_buffer, vtype = GRB.BINARY,name = "x")
     
    Regards,
    Simran
     
     
    0
  • Jirayu Bamroongwongsiri
    Gurobi-versary
    First Comment
    First Question

    Hello Simran,

    Thank you for the reply, but it still does not work. After I changed some codes to the following codes.

    I got the error "GurobiError: Invalid data in vars array"

    GurobiError                               Traceback (most recent call last)
~\AppData\Local\Temp\ipykernel_9928\2500881551.py in <module>
     29 #     max_completion_time[j] = m.addGenConstrMax(Max_Completion_Time[j],completion_time[i, j],name="Max_completion_time")
     30 
---> 31 Max_Completion_Time = m.addConstrs( (Max_Completion_Time[j] == gp.max_(completion_time[i, j] for i in Jobs) for j in Machines), name= "Max_Completion_Time")
     32 
     33 Tardy = m.addConstrs((Starting_job[i] + Processing[i] - 1 - Due_date[i] - aux1[i] == 0 for i in Jobs), name="aux_constr1.1")

src\gurobipy\model.pxi in gurobipy.Model.addConstrs()

src\gurobipy\model.pxi in gurobipy.Model.addConstr()

src\gurobipy\genexpr.pxi in gurobipy.GenExprMax._addAsConstr()

src\gurobipy\model.pxi in gurobipy.Model.addGenConstrMax()

GurobiError: Invalid data in vars array

    Best regards

    Jirayu

    0
  • Simranjit Kaur
    Gurobi Staff Gurobi Staff

    Hi Jirayu,

    The error you are seeing is coming from another part of your code.

    First, let's note that gp.max_ method takes a variable, a list of variables, or a tupledict of variables as arguments.

    Now, let's look at the following line of your code.

    completion_time[i,j] = Starting_job[i]+Processing[i]

    This makes completion_time[I,j] a LinExpr, which is not supported by the gp.max_method as an argument; hence, you see the error.

    Also, the above line of code will not give the desired completion time of i on a machine j. For example, let's say we have two machines and one job. Suppose the job starts at time 1 on machine 1 and has a processing time of 5. So, as per your code, Starting_job[i] will be 1, and the completion time of the job on both machine 1 and machine 2 is 6, which is incorrect

    One way to fix this will be to define completion_time[i,j] as variables

    completion_time = m.addVars(Jobs, Machines,vtype=GRB.CONTINUOUS, name="completion_time")

    and replace

    completion_time[i,j] = Starting_job[i]+Processing[i]

    with the following constraints that calculate the completion time of a job on a machine using your "s" variables that indicate whether a job starts on the machine and at what time.

    completion_time_constr =  m.addConstrs(( completion_time[i,j] == gp.quicksum( (k+Processing[i]) * s[i,j,k]  for k in Times ) for i in Jobs for j in Machines), name="completion_time")

    Regards,

    Simran

    0
  • Jirayu Bamroongwongsiri
    • Edited
    Gurobi-versary
    First Comment
    First Question

    Hello Simran,

    Thank you for fixing my wrong code. Your code is perfect, but I got the new problem after I calculate the idle time.

    Total_ET = gp.quicksum(Earliness_i[i] for i in Jobs) + gp.quicksum(Tardiness_i[i] for i in Jobs)
    Total_Idel_Time = gp.quicksum(Max_Completion_Time[j] for j in Machines)+ gp.quicksum(Processing[i] for i in Jobs)

    m.setObjectiveN(Total_Idel_Time, index=1, priority = 1, name = "Total_Idel_Time")
    m.setObjectiveN(Total_ET, index=0, priority = 2, reltol = 0.4 , name = "Total_ET")
    TypeError                                 Traceback (most recent call last)
~\AppData\Local\Temp\ipykernel_4332\2182328771.py in <module>
      1 Total_ET = gp.quicksum(Earliness_i[i] for i in Jobs) + gp.quicksum(Tardiness_i[i] for i in Jobs)
----> 2 Total_Idel_Time = gp.quicksum(Max_Completion_Time[j] for j in Machines)+ gp.quicksum(Processing[i] for i in Jobs)
      3 
      4 m.setObjectiveN(Total_Idel_Time, index=1, priority = 1, name = "Total_Idel_Time")
      5 m.setObjectiveN(Total_ET, index=0, priority = 2, reltol = 0.4 , name = "Total_ET")

src\gurobipy\gurobi.pxi in gurobipy.quicksum()

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

    It is about the unsupported code for 'gurobipy.LinExpr' and 'GenConstr'

    Best regards

    Jirayu

    0
  • Simranjit Kaur
    Gurobi Staff Gurobi Staff

    Hi Jirayu,

    One can only sum constants, Var objects, LinExpr objects, or QuadExpr objects using the quicksum() method.

    You are getting the error

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

    as Max_Completion_Time[j] is a general constraint object in the quicksum below

    gp.quicksum(Max_Completion_Time[j] for j in Machines)

    Please name your constraint differently from the variable names

    Max_Completion_Time_constrs = m.addConstrs( (Max_Completion_Time[j] == gp.max_(completion_time[i, j] for i in Jobs) for j in Machines), name= "Max_Completion_Time")

    Regards,

    Simran

    0
  • Jirayu Bamroongwongsiri
    Gurobi-versary
    First Comment
    First Question

    Thank you Simran I really appreciate your help. It's perfect.

    0
  • Sayem Ahmed
    Gurobi-versary
    First Comment

    Hi All,
    I have few more questions in accordance with the discussion -

    1. What if I need to calculate maximum completion time of each job (where each job has different no of operations, i.e., job 1 has 3 operations, job 2 has 2 operations), so that I can calculate tardiness and earliness based on delivery time window, for e.g., [a_i, b_i] = [18, 24].

    2. How to consider setup time of machines, delay time of machines and transportation time between machines while calculating makespan?

    0

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