Sabado, Marso 21, 2015

Solver

Excel includes a tool called solver that uses techniques from the operations research to find optimal solutions for all kind of decision problems.


1. On the green File tab, click Options.
 
2. Under Add-ins, select Solver Add-in and click on the Go button.
Click Solver Add-in
3. Check Solver Add-in and click OK.
Check Solver Add-in
4. You can find the Solver on the Data tab.
Click Solver

Formulate the Model

The model we are going to solve looks as follows in Excel.
Formulate the Model
1. To formulate this linear programming model, answer the following three questions.
a. What are the decisions to be made? For this problem, we need Excel to find out how much to order of each product (bicycles, mopeds and child seats).
b. What are the constraints on these decisions? The constrains here are that the amount of capital and storage used by the products cannot exceed the limited amount of capital and storage (resources) available. For example, each bicycle uses 300 units of capital and 0.5 unit of storage.
c. What is the overall measure of performance for these decisions? The overall measure of performance is the total profit of the three products, so the objective is to maximize this quantity.
2. To make the model easier to understand, name the following ranges.
Range NameCells
UnitProfitC4:E4
OrderSizeC12:E12
ResourcesUsedG7:G8
ResourcesAvailableI7:I8
TotalProfitI12


3. Insert the following three SUMPRODUCT functions.
Sumproduct Functions
Explanation: The amount of capital used equals the sumproduct of the range C7:E7 and OrderSize. The amount of storage used equals the sumproduct of the range C8:E8 and OrderSize. Total Profit equals the sumproduct of UnitProfit and OrderSize.

Trial and Error

With this formulation, it becomes easy to analyze any trial solution.
For example, if we order 20 bicycles, 40 mopeds and 100 child seats, the total amount of resources used does not exceed the amount of resources available. This solution has a total profit of 19000.
Trial Solution
It is not necessary to use trial and error. We shall describe next how the Excel Solver can be used to quickly find the optimal solution.

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