I'm trying to convert an AMPL model to Pyomo (something I have no experience with using). I'm finding the syntax hard to adapt to, especially the constraint and objective sections. I've already linked my computer together with python, anaconda, Pyomo, and GLPK, and just need to get the actual code down. I'm a beginner coder so forgive me if my code is poorly written. Still trying to get the hang of this!
Here is the data from the AMPL code:
set PROD := 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30;
set PROD1:= 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30;
ProdCost 414 3 46 519 876 146 827 996 922 308 568 176 58 13 20 974 121 751 130 844 280 123 275 843 717 694 72 413 65 631
HoldingCost 606 308 757 851 148 867 336 44 364 960 69 428 778 485 285 938 980 932 199 175 625 513 536 965 366 950 632 88 698 744
Demand 105 70 135 67 102 25 147 69 23 84 32 41 81 133 180 22 174 80 24 156 28 125 23 137 180 151 39 138 196 69
And here is the model:
set PROD; # set of production amounts
set PROD1; # set of holding amounts
param ProdCost {PROD} >= 0; # parameter set of production costs
param Demand {PROD} >= 0; # parameter set of demand at each time
param HoldingCost {PROD} >= 0; # parameter set of holding costs
var Inventory {PROD1} >= 0; # variable that sets inventory amount at each time
var Make {p in PROD} >= 0; # variable of amount produced at each time
minimize Total_Cost: sum {p in PROD} ((ProdCost[p] * Make[p]) + (Inventory[p] * HoldingCost[p]));
# Objective: minimize total cost from all production and holding cost
subject to InventoryConstraint {p in PROD}: Inventory[p] = Inventory[p-1] + Make[p] - Demand[p];
# excess production transfers to inventory
subject to MeetDemandConstraint {p in PROD}: Make[p] >= Demand[p] - Inventory[p-1];
# Constraint: holding and production must exceed demand
subject to InitialInventoryConstraint: Inventory[0] = 0;
# Constraint: Inventory must start at 0
Here's what I have so far. Not sure if it's right or not:
from pyomo.environ import *
demand=[105,70,135,67,102,25,147,69,23,84,32,41,81,133,180,22,174,80,24,156,28,125,23,137,180,151,39,138,196,69]
holdingcost=[606,308,757,851,148,867,336,44,364,960,69,428,778,485,285,938,980,932,199,175,625,513,536,965,366,950,632,88,698,744]
productioncost=[414,3,46,519,876,146,827,996,922,308,568,176,58,13,20,974,121,751,130,844,280,123,275,843,717,694,72,413,65,631]
model=ConcreteModel()
model.I=RangeSet(1,30)
model.J=RangeSet(0,30)
model.x=Var(model.I, within=NonNegativeIntegers)
model.y=Var(model.J, within=NonNegativeIntegers)
model.obj = Objective(expr = sum(model.x[i]*productioncost[i]+model.y[i]*holdingcost[i] for i in model.I))
def InventoryConstraint(model, i):
return model.y[i-1] + model.x[i] - demand[i] <= model.y[i]
InvCont = Constraint(model, rule=InventoryConstraint)
def MeetDemandConstraint(model, i):
return model.x[i] >= demand[i] - model.y[i-1]
DemCont = Constraint(model, rule=MeetDemandConstraint)
def Initial(model):
return model.y[0] == 0
model.Init = Constraint(rule=Initial)
opt = SolverFactory('glpk')
results = opt.solve(model,load_solutions=True)
model.solutions.store_to(results)
results.write()
Thanks!
The only issues I see are in some of your constraint declarations. You need to attach the constraints to the model and the first argument passed in should be the indexing set (which I'm assuming should be model.I).
def InventoryConstraint(model, i):
return model.y[i-1] + model.x[i] - demand[i] <= model.y[i]
model.InvCont = Constraint(model.I, rule=InventoryConstraint)
def MeetDemandConstraint(model, i):
return model.x[i] >= demand[i] - model.y[i-1]
model.DemCont = Constraint(model.I, rule=MeetDemandConstraint)
The syntax that you're using to solve the model is a little out-dated but should work. Another option would be:
opt = SolverFactory('glpk')
opt.solve(model,tee=True) # The 'tee' option prints the solver output to the screen
model.display() # This will print a summary of the model solution
Another command that is useful for debugging is model.pprint(). This will display the entire model including the expressions for Constraints and Objectives.