[R-SIG-Finance] Mixed integer programming

[Hannu Kahra]

Hi Eric,

thank you very much.

Best regards,
Hannu

On Tue, Feb 19, 2019 at 4:02 PM Eric Berger <ericjberger using gmail.com> wrote:

> Hi Hannu,
> I figured out the problem. The following code works for me. Note that I
> generally find it helpful to write function calls with the name of the
> package they come from, as in ompr::MIPModel() rather than just MIPModel().
> This is partly style and partly to avoid issues when functions get masked
> by other functions of the same name.
>
> Here is my code:
>
> library(magrittr)
> library(ompr)
> library(ROI)
> library(ROI.plugin.glpk)
> library(ompr.roi)
>
> mymodel <- ompr::MIPModel() %>%
>   add_variable(x[i], i = 1:7, type = "binary") %>%
>
> set_objective(200*x[1]+30*x[2]+200*x[3]+60*x[4]+50*x[5]+100*x[6]+50*x[7])
> %>%
>
> add_constraint(100*x[1]+20*x[2]+150*x[3]+50*x[4]+50*x[5]+150*x[6]+150*x[7]
> <= 500)
>
> z <- ompr::solve_model(mymodel, ompr.roi::with_ROI(solver="glpk"))
>
> z
> # Status: optimal
> # Objective value: 610
>
> summary(z)
> #                                   Length  Class              Mode
> #model                              3      optimization_model list
> #objective_value               1      -none-             numeric
> #status                              1      -none-             character
> #solution                           7      -none-             numeric
> #solution_column_duals   1      -none-             function
> #solution_row_duals         1      -none-             function
>
> z$solution
>
> # x[1] x[2] x[3] x[4] x[5] x[6] x[7]
> #   1    0    1    1    1    1    0
>
> HTH,
> Eric
>
>
> On Tue, Feb 19, 2019 at 3:46 PM Enrico Schumann <es using enricoschumann.net>
> wrote:
>
>> >>>>> "Hannu" == Hannu Kahra <hkahra using gmail.com> writes:
>>
>>     Hannu> I have tried to replicate Example 5.1 in Luenberger:
>> Investment Science.
>>     Hannu> Here is the model
>>     Hannu> model <- MIPModel() %>%
>>     Hannu>   add_variable(x[i], i = 1:7, type = "binary") %>%
>>     Hannu>
>>  set_objective(200*x[1]+30*x[2]+200*x[3]+60*x[4]+50*x[5]+100*x[6]+50*x[7])
>>     Hannu> %>%
>>
>>     Hannu>
>> add_constraint(100*x[1]+20*x[2]+150*x[3]+50*x[4]+50*x[5]+150*x[6]+150*x[7]
>>     Hannu> <= 500)
>>     Hannu> solve_model(with_ROI("glpk",verbose = TRUE))
>>
>>     Hannu> I get the following error
>>
>>     Hannu> Error in UseMethod("solve_model") :
>>     Hannu>   no applicable method for 'solve_model' applied to an object
>> of class
>>     Hannu> "function"
>>
>>     Hannu>  modelMixed integer linear optimization problem
>>     Hannu> Variables:
>>     Hannu>   Continuous: 0
>>     Hannu>   Integer: 0
>>     Hannu>   Binary: 7
>>     Hannu> Model sense: maximize
>>     Hannu> Constraints: 1
>>
>>     Hannu> What is wrong? Thank you in advance.
>>
>>     Hannu> -Hannu
>>
>> If you want people to help you, you need to provide a
>> reproducible example. Also, please do not post in HTML,
>> as code examples get scrambled and become unreadable.
>>
>> (If I had to venture a guess, I'd think you've
>>  forgotten one of those `%>%` before 'solve_model'.)
>>
>>
>> --
>> Enrico Schumann
>> Lucerne, Switzerland
>> http://enricoschumann.net
>>
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>

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