my small program give a wrong result

  • 14 March 2020
  • 2 replies

Dear all

My mathematical problem is to schedule the device in a home to achieve the minimum cost during a day. I divide a day into 24 time slots.  Each device with have its own Power rate and length of operation time. Main variables in my problem are starting time of devices at which a device is started to run. When I run my program, starting times of devices are always at time slot 1 and these are wrong results. I do not know why my program give wrong results.

Here is my program

Model Main_Test_starting_time {
    Set Time {
        Index: t;
    Set Devices {
        Index: d;
    Parameter Price {
        IndexDomain: t;
    Parameter Power_rate {
        IndexDomain: d;
    Parameter Length_of_operation_time {
        IndexDomain: d;
    Variable Starting_time {
        IndexDomain: d;
        Range: {
    Variable Energy_consumtion {
        IndexDomain: t;
        Range: nonnegative;
        Definition: sum[d, if Ord(t) >= Starting_time(d) AND Ord(t) <= Starting_time(d) + Length_of_operation_time(d) - 1 then Power_rate(d) else 0 endif];
    Variable Total_cost {
        Range: free;
        Definition: sum[t, Energy_consumtion(t) * Price(t)];
    Constraint Contraint {
        IndexDomain: d;
        Definition: Starting_time(d) <= Card(Time) - Length_of_operation_time(d) - 1;
    MathematicalProgram Minimum_Total_cost {
        Objective: Total_cost;
        Direction: minimize;
        Constraints: AllConstraints;
        Variables: AllVariables;
        Type: Automatic;

Please help me

Thank you very much



Best answer by mohansx 17 March 2020, 23:50

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2 replies

Userlevel 5
Badge +5

The wrong results is likely because you are using the variable Starting_time(d) as the condition of an IF block. From the formulation, looks like a device can be turned on only once during the day ? Using binary variables to represent on/off states is a very common formulation practice. Can you test your data on the attached model ? 

Thank you very much for your help. I learn a lot from your code. 

Now I know that we should avoid using if.. then..else as much as possible in mathematical program. 


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