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: {
            {1..inf}
        }
    }
    Variable Energy_consumtion {
        IndexDomain: t;
        Range: nonnegative;
        Definition: sumnd, 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: sumÂt, 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