Different Dual values?

Awaiting user input

Sanjeev Bhurtyal

September 19, 2021 18:39

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Why do I get different dual values for the same problem when I use model.getAttr("Pi", constraint list) and model.getConstrbyName("Constraint Name").pi?

mdlSP = gurobipy.model("Problem")
#1st Formulation
for j in jc:
    for c in co:
        for t in tm:
            Supply[j,c,t] =mdlSP.addConstr((quicksum(ot[j,jdash,c,t]for jdash in jc)+
                            quicksum(cta[j]*cta[jdash]*orr[j,jdash,c,t]for jdash in jc)+
                            quicksum(EC[equ,c]*xt[j,i,c,t,equ]for i in ip  for equ in eq)+
                            quicksum((EC[equ,c]*pta[i]*cta[j]*xr[j,i,c,t,equ])for i in ip for equ in eq)<=
                            q[j,c,t]), name = "Supply_%s_%s_%s"%(j,c,t))

#Get Dual
mdlSP.getAttr('Pi',Supply)


#2nd Formulation
#Constraint:
for j in jc:
    for c in co:
        for t in tm:
            mdlSP.addConstr((quicksum(ot[j,jdash,c,t]for jdash in jc)+
                            quicksum(cta[j]*cta[jdash]*orr[j,jdash,c,t]for jdash in jc)+
                            quicksum(EC[equ,c]*xt[j,i,c,t,equ]for i in ip  for equ in eq)+
                            quicksum((EC[equ,c]*pta[i]*cta[j]*xr[j,i,c,t,equ])for i in ip for equ in eq)<=
                            q[j,c,t]), name = "Supply_%s_%s_%s"%(j,c,t))

#Get Dual
     for j in jc:
         for c in co:
             for t in tm:
                 nu[j,c,t] = mdlSP.getConstrByName("Supply_%s_%s_%s"%(jdash,c,t)).pi

0

• Official comment

  

  Simranjit Kaur

  • Gurobi Staff

  June 23, 2025 02:47 Edited

  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?.
• 

  Matthias Miltenberger

  • Gurobi Staff

  September 20, 2021 08:01

  Hi Sanjeev!

  Could you please try posting a minimal reproducible example (MRE)?

  Thanks,
  Matthias

   

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