Each day, electrical utilities must decide on which power generators to start up and how much power each will generate. One utility has three generators with the following characteristics.
where 
is the fixed startup cost for starting generator i,
is the fixed cost per period of operation, 
is the cost per
period per megawatt generated, and 
is the maximum capacity, in megawatts,
that can be generated each period by generator i.
There are two periods in a day and the number of megawatts needed is 2900 in the first period and 3900 in the second period. A generator started in the first period can be used in the second period without incurring an additional startup cost. All generators are turned off at the end of the day.
Formulate this problem.