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Monday, January 19, 2015

Operations Research

We are allowed to use our computers. The midterm will be all about excel and geogebra. We will be going back to Multi-criteria decision making as well as product mixes.

MCDM 
You have a decision to make, like choosing, which ice cream flavor to eat, picking a cell phone plan, to even selecting a college to attend.

As a previous assignment, I chose which cell phone to purchase based on processer speed, RAM, battery life, and more. read about it here. I am using it as my example for the explanation below.

In my case, the criteria is the features of the phone.

For the next table, you need to collect data. I already did: (I chose the smallest possible choice for the storage size.) 




This part is where we do continuous vs. categorical measures.


We need to rescale the categorical measures.(I removed the moto x, because it isn't available on sprint) 1 is the best, 0 is the worst).

Now, we are rescaling everything. This is perhaps the hardest part (besides weighting ), so pay attention!

For the continuous measures, We make a scale. Put the most desirable size on the left and the worst on the right. This is how mine looks after I finished the rear cameras: (I suggest you use a notepad instead of your computer for this part). Remember, you can assign the best and worst scores, as long as your numbers fit in between.


After you have a number line like this, start doing the math. Let's start with the GS5.
Basically, it's the (score of the item - the worst possible score) divided by (the best possible score - worst possible score). Then, just do the division and you are there! Repeat this step for all the variables...

Here is the chart finished, with the pre- weighted scores.

 Pre-weighted, all the measures are on the same level. But, I value the battery life more than the camera. Here comes the ranks: rank each measure on the importance to you. and assign points (up to 100) based on importance (higher points= more important).

Like it's written, the weight is points/sum . The excel formula to get the weights is  =SUMPRODUCT(F77/$F88) and drag it down. For the Sum: it is =SUM(F77:F87)


Now, we are going to apply the weights. I copied the pre-weight table and the weights, then multiplied the weight for each category times the devices

I'll show you the formulas: (zoom in for a better view)

That is Multi Criteria Decision Making folks.

Geogebra

We use it for calculating limits on product mixes. It is limited to 3 products (3d), then we will go back to excel for more)

Here is a problem from the homework in Geogebra. It is the Anderson Cell Phone Company.

Two products, smartphone and standard phones. 10 workers, work 7 hours a day. smartphone takes 2.5 minutes to assemble. standard phone takes 1.5 minutes to make. Company receives 2000 LCD screens. Profit from smartphone is $40 and $30 from standard phone.

I plugged it into Geogebra:
With geogebra, you can see your limits. But, the problem is that you need to find the answer, by sliding the slider. It takes a long time to get it perfect.

That's why I put it in excel. I used Solver to generate the total profit for me.


Here is it showing the formulas.
Here is solver in action:



Good luck on your exam. If you have any questions or comments, leave a comment below. 

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