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D2 6th June 2013 Watch

1. Can someone do this question please and tell me what they get, the mark scheme seems to be wrong, i get different answers
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2. (Original post by Knoyle quiah)
Well done, what were the 4 marks you lost? also where do i get these practice papers?
There are some here http://www.thestudentroom.co.uk/show....php?t=2013301
Smith
3. (Original post by Knoyle quiah)
Can someone do this question please and tell me what they get, the mark scheme seems to be wrong, i get different answers
I got A should play I with probability 1/3 and II with probability 2/3 and the value of the game to A is 11/3. Is that right?
Smith
4. (Original post by Knoyle quiah)
Can someone do this question please and tell me what they get, the mark scheme seems to be wrong, i get different answers
I just got these

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5. (Original post by Hamburglar)
Good idea!

-Forgetting to reduce columns in the Hungarian algorithm. I don't know if it is just me, but I forget this so many times and it is so frustrating.

-To find the value of a game, sub p back into one of the equations you used to calculate it, and not just any equation, like the unused one. To check, put it in the other equation you used and it should give the same value.

-Always read if it is maximising or minimising hungarian.

-Remember to give answers in real terms. If the question says at the start, here are costs in £'000s, make sure you multiply your final answer by 1000.

These aren't mistakes I've made per se, but just things to look out for

That's all for now
common ones I see...

Transport linear Prog, forgetting Xij >= 0 and not putting enough detail into the defining at the start.

Game Theory - when a row has been dominated in part a) forgetting A never plays row ... in the final solution.

Not stating value of RMST, drawing is necessary but certainly advisable.
6. (Original post by Knoyle quiah)
How does everyone find max flow=min cut?? it takes me soo long by doing trial and error of possible cuts, does it take people long normally?
after you have completed your flow augmenting routes, you will probably need to draw out a flow diagram. If it doesn't ask you for one adapt the diagram in the question.

Now take out a highlighter and highlight all the saturated arcs, it should then take seconds to spot a cut only passing through the highlighted lines. Sometimes it will also have to pass through an empty arc from sink to source mind.
7. (Original post by Lilmzbest)
Oh...hmm i shall have to go trawling through old papers to try and find one of these questions, can't find any in the book

...Am i being stupid because i can't even get my head around how that would work?
you can get them in table form, the ones where you have about 3 tables to look at; one will give costs of travelling to and from locations, one will give profit made at those venues etc

it could then say find a maximin route for profit etc.
8. (Original post by Arsey)
I just got these

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Yeah same as what i got, but mark scheme is wrong for this question, thanks.
9. (Original post by Arsey)
common ones I see...

Transport linear Prog, forgetting Xij >= 0 and not putting enough detail into the defining at the start.

Game Theory - when a row has been dominated in part a) forgetting A never plays row ... in the final solution.

Not stating value of RMST, drawing is necessary but certainly advisable.
Do you mean drawing isn't necessary?
10. (Original post by Arsey)
after you have completed your flow augmenting routes, you will probably need to draw out a flow diagram. If it doesn't ask you for one adapt the diagram in the question.

Now take out a highlighter and highlight all the saturated arcs, it should then take seconds to spot a cut only passing through the highlighted lines. Sometimes it will also have to pass through an empty arc from sink to source mind.
Ahh this explains why i take so long to do these, i usually skip drawing the final flow pattern and just do it from the original graph, thank you .
11. (Original post by smith50)
Could someone give me examples of a travelling salesman problem and network flows please
Thanks,
Smith
example of travelling salesman?

anything involving what a travelling salesman would have to do.

A hospital drug rep has to visit 10 different hospitals, objective is to find the smallest range of values for the shortest distance this is possible visiting each hospital at least once.....

12. (Original post by knowledgecorruptz)
Do you mean drawing isn't necessary?
yes I do.

The only reason you should draw it (with the extra arcs) is to see if the solution is possible which tells you if it is < or <=

I don't think I have ever seen a <= one though as that would be the optimal solution.
13. Anyone have any tips for not making any errors in simplex?? i know everyone uses same method, but how to minimise mistakes?
14. (Original post by Knoyle quiah)
Yeah same as what i got, but mark scheme is wrong for this question, thanks.

there are a few errors on the MS for the mock / specimen papers. I don't think there are any on the official MS for the actual papers though.
15. (Original post by Knoyle quiah)
Anyone have any tips for not making any errors in simplex?? i know everyone uses same method, but how to minimise mistakes?
I would always advise the longer, 2 tables per iteration, method. Check any fractions using a calc.
16. (Original post by Arsey)
there are a few errors on the MS for the mock / specimen papers. I don't think there are any on the official MS for the actual papers though.
Havnt seen any in the official d2 edexcel papers, but have come across a couple of errors in the old edexcel d1 papers
17. (Original post by smith50)
I got A should play I with probability 1/3 and II with probability 2/3 and the value of the game to A is 11/3. Is that right?
Smith
yeah correct mark scheme wrong
18. (Original post by Arsey)
I would always advise the longer, 2 tables per iteration, method. Check any fractions using a calc.
That's what I do. I just make too many mistakes when I try and do it all using one table, and it probably takes me more time to use one table as I have to think more carefully about what i'm doing.
19. (Original post by brittanna)
That's what I do. I just make too many mistakes when I try and do it all using one table, and it probably takes me more time to use one table as I have to think more carefully about what i'm doing.
What do u mean 2 tables per iteration? so for example, 2 tables of the exact same iteration (theoretically same values) to double check values??
20. (Original post by Arsey)
you can get them in table form, the ones where you have about 3 tables to look at; one will give costs of travelling to and from locations, one will give profit made at those venues etc

it could then say find a maximin route for profit etc.
Oh i thought it meant the building thing type questions where values depend on what's already been built... i thought that was maximin

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