constraint the future state of a decision variable

Answered

carlos saenz

December 23, 2022 04:21 Edited

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Hi guys, 

Im trying to constraint state of a descicion variable but Im having problems please help and thank you!

for t in T:

  for i in R:

    if t==0:

    

      m.addConstr((v_r[(i,t)]),gb.GRB.EQUAL,(data['Reservoir'][i]['Vmin'])+(data['Demand'][t]['Wat_inflow_r0'])-(w_s[(i,t)])-(w_d[(i,t)]),name="Volume in t+1 {}{}".format(i,t))

  # restriction demand supply

    else:

      m.addConstr((v_r[(i,t)]),gb.GRB.EQUAL,(v_r[(i,t-1)])+(data['Demand'][t-1]['Wat_inflow_r0'])-(w_s[(i,t-1)])-(w_d[(i,t-1)]),name="Volume in t+1 {}{}".format(i,t))

 

when I try to do this 

else:

      m.addConstr((v_r[(i,t+1)]),gb.GRB.EQUAL,(v_r[(i,t)])+(data['Demand'][t]['Wat_inflow_r0'])-(w_s[(i,t)])-(w_d[(i,t)]),name="Volume in t+1 {}{}".format(i,t))# esto esta mal el estado t+1 del volumen debe depender del estado anterior 

  

the error is TypeError: can only concatenate str (not "int") to str

  

Related to

• Python

0

• Official comment

  

  Simranjit Kaur

  • Gurobi Staff

  November 13, 2026 01:51

  This post is more than two 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 try Gurobot, our chatbot interface offering instant, expert-level support.
• 

  Maliheh Aramon

  • Gurobi Staff

  December 24, 2022 03:04

  Hi Carlos, 

  This is a Python error and it happens when you try to add an integer to a string.

  Since you are using the str.format() method, the error should not be related to the constraint names. 

  What are the values of the set \(\texttt{T}\)? If this set includes string values, \(\texttt{t+1}\) in \(\texttt{v_r[(i,t+1)]}\) can cause the error. 

  In case you need more help, please post a minimum working example.

  Best regards,

  Maliheh

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