You are Here: Home >< Maths

# Edexcel D2 Transportation Problem

Announcements Posted on
Would YOU be put off a uni with a high crime rate? First 50 to have their say get a £5 Amazon voucher! 27-10-2016
1. Hi, I am self-teaching D2 and am having trouble grasping how to obtain an improved solution using the stepping-stone method. The question gives a table of costs, and I have firstly used the north-west corner method of getting an initial solution. I have calculated improvement indices, but do not know how to pick a loop in order to improve my solution.

The original question, and my initial solution are shown in the picture, and I have calculated improvement indices
I 1,2 = 2
I 1,3 = 0
I 3,1 = -1
I 3,2 = 2

I'm slightly stuck how to carry on, and any help would be really great, thanks!
Attached Images

2. The index on (3,1) is negative so you want to send goods along that route.

Use the stepping stone method. There's only one possibility: in the initial solution, add x to box (3,1), subtract x from box (2,1), add x to box (2,3) and subtract x from box (3,3). Then pick x to be as large as possible so as to not make any of the boxes in the new solution negative. Then re-test for optimality.
3. That's really great help, but how do you know which squares you can use? I don't quite understand the rules for the stepping stone method. Thanks
4. Try to think about what exactly it is you're doing when you use the stepping stone method.
You want to add x items to the route with negative index (that's row 3, column 1). In order to keep the total demand on column 1 in check you need to also subtract x from somewhere in column 1. Similarly, you need to subtract x from somewhere in row 3. And then you keep doing this until everything adds up again. And don't add or subtract from any unused cells except the one you started with.

Have a look at the wiki: http://www.thestudentroom.co.uk/wiki...tion_Algorithm
5. wow, thank-you so much, that's a great help

## Register

Thanks for posting! You just need to create an account in order to submit the post
1. this can't be left blank
2. this can't be left blank
3. this can't be left blank

6 characters or longer with both numbers and letters is safer

4. this can't be left empty
1. Oops, you need to agree to our Ts&Cs to register

Updated: September 28, 2007
TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Today on TSR

Find out here

Poll
Useful resources

### Maths Forum posting guidelines

Not sure where to post? Read here first

### How to use LaTex

Writing equations the easy way

### Study habits of A* students

Top tips from students who have already aced their exams