How can I decrease number of variables using m.addVars ul and lb

[Taner Cokyasar]

Hello,

I am defining variables "x" with subscripts i = 1:3 and c = 1: 5  using m.addVars.

After defining i and c, I have the following:

x = m.addVars(i, c, obj = x, name="x")

This will generate x_11,     x_12,   ....,    x_15,  .....................................   x_31, x_22, ........, x_35

However, I know that for i=1,  I need only x_12 and x_13     

                                  for i=2, I need only x_23 and x_24  

                                  for i=3, I need only x_34 and x_35   others are redundant variables.

c_i should be a new list containing consecutive integer numbers:

c_i = P_i -1,    P_i

where P_i is another parameter for each i.

P_1 = 3 

P_2 = 4

P_3 = 5

c_i is giving me the pairs that I need to use in my variable generation. But, I don't know how I will create c_i (in tuples or?) and then create x variables based on it.

Any suggestions are appreciated.

Best regards,

[Hervé Audren]

I think the solution here is to only add the relevant variables. How about using something like:
P = [3, 4, 5]
x = [(m.addVar(name="x_{}{}".format(i+1,j-1)), m.addVar(name="c_{}{}".format(i+1,j))) for i,j  in enumerate(P)]

x is then a list of tuples:
x = [(x_12, x_13), (x_23, x_24), (x_34, x_35)]

[Daniel Espinoza]

You can also define the list of relevant tuples and use that list to define the variables

[Taner Cokyasar]

Thank you very much! It definitely makes sense. However, I am using dictionaries for all my parameters. So, my P is in a dictionary. When I run the code, naturally it says:

Cannot mix scalar and tuple values in a tuplelist

Is there any way to apply this logic when P is a dictionary? Besides, I defined another dictionary for "1" as "d". is it possible code format(i+d, j-d)....?

Thanks again!

[Taner Cokyasar]

Nevermind, I just changed everything to lists and using the code you provided. Works fine! I will have some more questions. If you may have time to assist me, I would highly appreciate Herve Audren!

Thanks,

On Thursday, May 18, 2017 at 7:22:49 AM UTC-4, Hervé Audren wrote:

[Taner Cokyasar]

Hervé ,

Now, I need to add constraints for the binary variables you helped me to create as:

x_12 + x_13 = 1

x_23 + x_23 = 1

x_34 + x_35 = 1

Do you have any suggestion how to add these constraints based on your code? I tried sum.x, but it says lists cannot be added.

On Thursday, May 18, 2017 at 7:22:49 AM UTC-4, Hervé Audren wrote:

[Daniel Espinoza]

Hi Taner,

tuplelist has a select(1,'*') method that is way more efficient than looping in all variables and then select the relevant ones

You can look at http://www.gurobi.com/documentation/7.0/refman/py_tuplelist.html for details

Best

Daniel

[Taner Cokyasar]

Hi Daniel,

Thank you for your advice. I actually read tuplelist function and couldn't get how I am gonna apply it in my case. In this second look, I kind of got how I need to do; basically I will create pairs that I want to produce. Then, how can I addvariables stored in that tuplelist? Also, how can I do summation when i=1  and j is as I specified earlier? If you may tell me the functions, I will definitely change all my bariable constuction to this way due to efficiency.

Thanks,

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[Edgar Alan Avila Gomez]

Hello, you can do this model too easy using python or other lenguaje with Gurobi. 

x = {}

for i in range(3):

....j = i+1

....for n in range(2):

......x[i,j] = m.addvar(vtype=GRB.BINARY, name= "X_" + str(i+1) + "_" + str(j+1))

......j += 1

for i in range(3):

....m.addConstr(x[i,i+1] + x[i,i+2] == 1)

if you want to generalize the model, can use lists,  "for i in list"

For my point of view, it is more intuitive to use python + Gurobi

example = [m.addConstr(x[i,i+1] + x[i,i+2] == 1) for i in range(3)]

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ING. Edgar Alan Avila Gomez

[Taner Cokyasar]

Thank you for your respond, Edgar. I also have the following question that I posted on stackoverflow.com, but they couldn't really help me except for questioning my knowledge. If you guys can help me, I would really appreciate it.

Usually, variables are created with two complete indexes in Gurobi such as i=3 and j=2 yielding: x_11, x_12, x_21, x_22, x_31, x_32. However, I am trying to eliminate some redundant variables so as to decrease computation time. I have created the following variables with the following code:

from gurobipy import *
rangevalue = list(range(8,13))
I = 10
E = [6, 3, 4, 2, 4, 2, 5, 1, 4, 2]
m = Model("a")

for i in range(I):
    for k in range(len(rangevalue)):
        t = E[i]
        y[i+1, rangevalue[k] - t] = m.addVar(vtype=GRB.BINARY,
           name="y%s" % str([i+1, rangevalue[k] - t]))
m.update()
y

This yields following variables:

{(1, 2): <gurobi.Var y[1, 2]>,
 (1, 3): <gurobi.Var y[1, 3]>,
 (1, 4): <gurobi.Var y[1, 4]>,
 (1, 5): <gurobi.Var y[1, 5]>,
 (1, 6): <gurobi.Var y[1, 6]>,
 (2, 5): <gurobi.Var y[2, 5]>,
 (2, 6): <gurobi.Var y[2, 6]>,
 (2, 7): <gurobi.Var y[2, 7]>,
 (2, 8): <gurobi.Var y[2, 8]>,
 (2, 9): <gurobi.Var y[2, 9]>,
 (3, 4): <gurobi.Var y[3, 4]>,
 (3, 5): <gurobi.Var y[3, 5]>,
 (3, 6): <gurobi.Var y[3, 6]>,
 (3, 7): <gurobi.Var y[3, 7]>,
 (3, 8): <gurobi.Var y[3, 8]>,
 (4, 6): <gurobi.Var y[4, 6]>,
 (4, 7): <gurobi.Var y[4, 7]>,
 (4, 8): <gurobi.Var y[4, 8]>,
 (4, 9): <gurobi.Var y[4, 9]>,
 (4, 10): <gurobi.Var y[4, 10]>,
 (5, 4): <gurobi.Var y[5, 4]>,
 (5, 5): <gurobi.Var y[5, 5]>,
 (5, 6): <gurobi.Var y[5, 6]>,
 (5, 7): <gurobi.Var y[5, 7]>,
 (5, 8): <gurobi.Var y[5, 8]>,
 (6, 6): <gurobi.Var y[6, 6]>,
 (6, 7): <gurobi.Var y[6, 7]>,
 (6, 8): <gurobi.Var y[6, 8]>,
 (6, 9): <gurobi.Var y[6, 9]>,
 (6, 10): <gurobi.Var y[6, 10]>,
 (7, 3): <gurobi.Var y[7, 3]>,
 (7, 4): <gurobi.Var y[7, 4]>,
 (7, 5): <gurobi.Var y[7, 5]>,
 (7, 6): <gurobi.Var y[7, 6]>,
 (7, 7): <gurobi.Var y[7, 7]>,
 (8, 7): <gurobi.Var y[8, 7]>,
 (8, 8): <gurobi.Var y[8, 8]>,
 (8, 9): <gurobi.Var y[8, 9]>,
 (8, 10): <gurobi.Var y[8, 10]>,
 (8, 11): <gurobi.Var y[8, 11]>,
 (9, 4): <gurobi.Var y[9, 4]>,
 (9, 5): <gurobi.Var y[9, 5]>,
 (9, 6): <gurobi.Var y[9, 6]>,
 (9, 7): <gurobi.Var y[9, 7]>,
 (9, 8): <gurobi.Var y[9, 8]>,
 (10, 6): <gurobi.Var y[10, 6]>,
 (10, 7): <gurobi.Var y[10, 7]>,
 (10, 8): <gurobi.Var y[10, 8]>,
 (10, 9): <gurobi.Var y[10, 9]>,
 (10, 10): <gurobi.Var y[10, 10]>}

Now, I need to create the following constraint set:

y[1, 2] + y[1, 3] + y[1, 4] + y[1, 5] + y[1, 6] == 1
y[2, 5] + y[2, 6] + y[2, 7] + y[2, 8] + y[2, 9] == 1

For all values of variable i. My code directly works and shows what I am doing. If you may find a way to create these constraints either with addConstr and addConstrs functions, I would really appreciate it.

You can also view the same question on: http://stackoverflow.com/questions/44060485/gurobi-adding-constraints?noredirect=1#comment75172831_44060485

[Edgar Alan Avila Gomez]

for i in range(I):

m.addConstr(quicksum([y[i+1, rangevalue[k] - E[i]] for k in range(len(rangevalue))]) == 1)

or.

example = [[m.addConstr(quicksum([y[i+1, rangevalue[k] - E[i]] for k in range(len(rangevalue))]) == 1)

]for i in range(I)]

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[Taner Cokyasar]

I really appreciate it, Edgar. Now, I got the logic of using for loops inside the addConstr function.

Best,

Taner

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