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Mapping two sets and set alias

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4 comments

  • Silke Horn
    Gurobi Staff Gurobi Staff

    Hi Buddi,

    Welcome to Gurobi!

    To define sets, you can use anything that Python offers. E.g. you could define your sets using

    starting_city = {"City1", "City2", "City3"}

    and

    ending_city = starting_city

    If you have two sets (or lists or dictionaries) "hours" and "years", you can create a dictionary of variables using the addVars method:

    var = model.addVars(hours, years)

    This dictionary then contains one variable for each combination of hours and years, e.g.:

     var[hour, year]

    Does this answer your questions?

    Silke

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  • Charitha Buddhika Heendeniya
    Gurobi-versary
    Conversationalist
    Curious

    Hi Silke,

    Thank you for your reply. Let me show you a small example. 

    In the following image, I have defined several technologies (key) and several energy flows resulting from those technologies. So it is a one to many mapping between the technologies (pp_tech) and energy flow type (pp_type). 

    Now I have several variables. Here t is the set of time-steps. 

    v_power = model.addVars(t, pp_tech, pp_type, name="v_power", lb=0)

    v_chp_electricity = model.addVars(t, name="v_chp_electricity", lb=0)

    Now I want to write a constraint  that gives me only the electrical power flows from CHP plants. So I write,

    model.addConstrs((v_chp_electricity[t] == quicksum(quicksum(v_power[t,pt,pp] for pp in pp_type if pp=='chp_e')
    for pt in pp_tech) for t in T), name='c6.1') 

    But something goes wrong here and when I print the model I get something like this.

    c6.1[0]: v_chp_electricity[0] = 0
    c6.1[1]: v_chp_electricity[1] = 0
    c6.1[2]: v_chp_electricity[2] = 0
    c6.1[3]: v_chp_electricity[3] = 0
    c6.1[4]: v_chp_electricity[4] = 0
    c6.1[5]: v_chp_electricity[5] = 0
    c6.1[6]: v_chp_electricity[6] = 0
    c6.1[7]: v_chp_electricity[7] = 0
    c6.1[8]: v_chp_electricity[8] = 0

    Funnily enough, somewhere else in the model, I see variables such as,

    v_power[0,CHP,BESS]

    v_power[0,CHP,EL_HEATER]

    so clearly the mapping has not worked as I intended. Do you see what I'm doing wrong here? Thank you very much for your support. 

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  • Silke Horn
    Gurobi Staff Gurobi Staff

    There are a few things I find confusing:

    • In your dictionary, the values are strings. Maybe you want them to be arrays of strings instead? Then you could also access the individual entries. E.g.:
      {'CHP': ['chp_e', 'chp_h', 'chp_hw'], 'PV_PROOF': ['pv_proof'], ...}
    • How are pp_tech and pp_type defined?
    • What are t and T? In your constraint definition, you have "for t in T", which suggests that T is the set of timesteps. In your variable definitions, however, you use t.
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  • Charitha Buddhika Heendeniya
    Gurobi-versary
    Conversationalist
    Curious

    Dear Silke,

    Thank you very much.

    What are t and T? - You are correct, that was a typo. I had longer variable and set names in the actual code and I replaced them with short symbols when I copied them to my question to make it more clear. So T is the set of hours and t is a member of T. 

    I managed to find another way to do what I wanted to do. 

    Here I defined the technology (pp_tech) and energy flow type (pp_type) as a tuplelist. So chp_e --> (CHP, ELEC)

    With this, I can write the constraints I wanted to write. Thank you. 

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