How can I get or print the LHS constraint values?

Answered

Marcela Villa Marulanda

October 27, 2019 15:11

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Hello, I'm getting started in using gurobi-python and need help.  This is my first model  and I want to print or get the values of the LHS_Constr (see below):

from gurobipy import *

pp3=Model()
vrs=["Original","Cheddar","Wasabi"]
procs=["X-Ray","Checkweigher"]

RestrProc2={"X-Ray":{"Original":8.6, "Cheddar":2.2, "Wasabi":5.1},
"Checkweigher":{"Original":7, "Cheddar":6.8, "Wasabi":9.8}}

MCapcity={"X-Ray":480,"Checkweigher":540}

PV={"Original": 20, "Cheddar":15, "Wasabi":17}

CostProc={"X-Ray":0.11,"Checkweigher":0.22}

Vrbl=pp3.addVars(vrs,name="Cheese")

#Objective function

FnOb=quicksum(PV[vr]*Vrbl[vr] for vr in vrs)-quicksum(CostProc[proc]*RestrProc2[proc][vr]*Vrbl[vr] for vr in vrs for proc in procs)
pp3.setObjective(FnOb,GRB.MAXIMIZE)

#Constraints

LHS_Constr=(quicksum(RestrProc2[proc][vr]*Vrbl[vr] for vr in vrs)<=MCapcity[proc] for proc in procs)
pp3.addConstrs(LHS_Constr, name="Capacity")

pp3.optimize()
pp3.printAttr('X')

 

I appreciate your support.

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• Official comment

  

  Simranjit Kaur

  • Gurobi Staff

  December 06, 2024 00:52

  This post is more than three 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 why not try our AI Gurobot?.
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  Eli Towle

  • Gurobi Staff

  October 28, 2019 22:16

  Hi Marcela,

  Do you mean you want to extract the values of the LHS of those constraints at the optimal solution? If so, you can do this as follows:

  1. Construct a LinExpr object for each of the LHS expressions
  2. After optimizing, evaluate each LHS expression with the LinExpr.getValue() method

  In your case:

  LHS = {proc : quicksum(RestrProc2[proc][vr]*Vrbl[vr] for vr in vrs) for proc in procs}
  pp3.addConstrs(LHS[proc] <= MCapcity[proc] for proc in procs)
  
  pp3.optimize()
  
  for proc in procs:
      print(LHS[proc].getValue())

  I hope this helps!

  Eli

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  Marcela Villa Marulanda

  October 30, 2019 10:45

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  Hi Eli, it worked! Thank you very much.  

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  Wenbo Ma

  August 15, 2021 02:46

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  Just add a note to Eli's answer:

  If you don't want to create a new object LHS, below can give you the values too.

  for proc in procs:
      quicksum(RestrProc2[proc][vr]*Vrbl[vr] for vr in vrs).getValue()

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