Mapping two sets and set alias
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Dear community,
I'm used to using GAMS for optimization problems and it has useful facilities that allows you to map two sets and define an alias to a set. For example, if I have a set of locations and I call that set "starting_city", I can define a set called "ending_city" and make it an alias of the set "starting_city". Also if I have two sets called "hours" and "years", I can create a mapping between the two sets so that I can create variables such as var(hour, year).
How can I implement the same using the Gurobi-Python interface? I apologize if this is a really basic question.
Regards
Buddi
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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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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] = 0Funnily 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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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.
0 - 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.:
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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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