Solver with binary variable
 

Hello everyone!

I still got a problem with a Solver optimization. I hope you can help me.

There is a machine which can produce 2 products separately. In my
optimization problem there are several constraints:
- Sum of Production of X & Y is equal to or less than capacity of the machine

- Demand of X & Y must be satisfied (Stock (t-1) €“ Demand + Production +
Purchase €“ Stock (t) = 0 ) in each month

- Stocks must be equal to or less than maximum stock & not less than minimum
stock
- And:
o The production of Y should happen in batches of 500 (if 500 is lower
than capacity)
oThat means that Y is not produced each month. It is only produced, when
Stock of Y will be too low (Row: €œCalculated Production€�)

For the last constraint I implemented a binary variable which stands for
Production of Y Yes/No.
The objective is a minimization of fictive costs: The sum of Stocks * Stock
Costs + the sum of Production * Production Costs + Sum of Purchase * Purchase
Costs

I think I am still missing one or more constraints. You can have a look in
the example file.
1. There is a purchase of Y in February. Why not 0 in February and all the
required purchase in March?
2. There are also purchases of Y in May & June. Why not in July?
3. There is a purchase of X in March. But there is still free capacity in
March?

http://www.herber.de/bbs/user/66765.xls