D2 6th June 2013

depends on the question, if you have to find the best strategy for player B right from the start then I would certainly advise transposing the matrix.

However, if you have already found the best strategy for A, then you will be able to discard on of the lines for what B plays in the well diagram, meaning you could delete a column and just solve simultaneously.

Hey guys!

I need some help with question 5 of the D2 mock paper? Aren't the arrows in the diagram in the answer booklet wrong or something?

In June 08 question 6 they want you to use the nearest neighbour and prime without a table, would they ask us to do that in the new spec?


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When you have a degenerate solution on a transportation problem, which cell do you put the 0 in so you can work out shadow costs?

What is value of cut C2, can someone say and i will check ms, i cant get it for some reason

I'm not looking at it right now, but beware that mark schemes for mock papers and practice papers are generally very wrong. I do recall remembering that the mark scheme was wrong when labelling some arrows on one of those papers.



Yes possibly, June 2008 was part of the current spec as far as I know. It is pretty much the same idea anyway, so I don't see why they couldn't ask. Although I can't say I remember being asked to use Prim's, usually they ask you to use Kruskal's but either way, you should be comfortable with both.



As you're filling the table in, if supply and demand are satisfied at the same time, you can either go across one and put the 0 in the cell, then move down. Or, go down and put the 0 in that cell, and move along one. Basically in the diagonal you have, you want to put the zero in one of the spaces where normally you'd expect a number.

Technically you can actually put it anywhere, but it's best to stick to the rule of moving along and downwards only.



64 if I am not mistaken

Hey guys!

I need some help with question 5 of the D2 mock paper? Aren't the arrows in the diagram in the answer booklet wrong or something?

OK thank you, but i cant get it, your correct can u please say which arcs u used??

Sure

DH, DF, CE, GE, GI

24 + 8 + 10 + 18 + 4 = 64.

Make sure you are looking at the capacities of the arcs and also make sure that you are considering arcs that are flowing into the cut only. GE for example is flowing into the cut, as it is going in from the left side of the line, and coming out of the right side of the line.

I missed out GE, surely GE is going towards the source ?? I cant understand how GE is in the cut

It flows into the cut though, I'm not sure how to help you picture this, but I'll try give it a shot.

Consider that the cut, as actually a 3-dimensional object, like a path of train tracks and not just a line. Now, anything that goes through this object from left to right, is into the cut. Anything from right, to left is out of the cut.

Now if you run your finger down the tracks, towards where the track starts to veer off to the right towards GE, consider that the bottom of the tracks from how we look at it is the "left side" of the tracks. GE flows in towards this side, and therefore it goes across these train tracks from left to right and so it is into the cut.

I hope this helps

Thank you this has helped me to understand it better

What is an example of minimax/maximin problem in real life for dynamic programming??? could be asked

Hey there guys. I was wondering if somebody could clear one last thing up for me. June 2011, question 5, part (e): what format should the flow be shown in? I put all the flows on and circled saturated arcs (I remember seeing this done somewhere), but the mark scheme just has the numbers on their own. Should I just stick to the mark scheme on this one?

You're welcome



This has come up on an old past paper before, and here are the two examples on the mark scheme.

Maximin - Maximising the minimum length of an arc could be in a factory, where the rate of production depends on the slowest process. Therefore, to maximise the rate of production, you must maximise the slowest process. In this case, the length of the arc is the time it takes to complete the process.

Minimax - Minimising the maximum length can be in a system of airports. An airplane could have to transport cargo around a network, and so the longest distance has to be minimised. This is because fuel usage between airports is also minimised, which means more cargo can be carried. In this case, the arc length is the distance between the airports.

These examples can be found in the textbook too

Thank you this has helped me to understand it better