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# D1 edexcel jan 05 watch

1. how did it go
got 40 for the flows question
that's all I remember

oh and I think 20/3 for the z and y values after the second iteration in simplex
2. 40's familiar
ALLLLLL the past papers are easy compared to that pile of rubbish
40/100 seems to be the mark I will end up with
I just wanted to pick up my paper and rip it to shreds.
Teachers saying ooo yer you should all easily get 100 on D1 ( )
Ack what a moron!
3. Good exam. I guess i got fairly lucky as all my sorts of questions came up. Much easier than M3 at least.
Both myself and the other FM candidate got 40 for the flows question.
The third simplex table was not optimal and the profit was something like 1733+(1/3) too, IIRC.
4. lol guess our teacher was bad then!
Yep we learn't the OCR sylabus for an Edexcel exam!
5. (Original post by Gaz031)
Good exam. I guess i got fairly lucky as all my sorts of questions came up. Much easier than M3 at least.
Both myself and the other FM candidate got 40 for the flows question.
The third simplex table was not optimal and the profit was something like 1733+(1/3) too, IIRC.
Yep.. thats all correct

Only bits i was iffy on was: That algorithm you had to mention in the last part of the kruskals/prims question (2 i think?) - I said use dijkstra to find shortest path from either of the verticies of the laid paths to the shortest path found using prims/kruskals.
And also the Route Inspection one (Q 5) I went for Eularian. .start at A end at A as A was already even (they didn't specify :'( - i think ) - is that right? Now that i think about it.. think it was A -H.. you need to make A and H odd

Also in the way of answers.. the bin-packing one.. 5 bins.. and it was optimal..hmm..
And the weight of best path to take was in the region if one thousand four hundred- can't remember it exactly but the weight of repeated edges was 240 - i hope

I actually enjoyed that paper! - coming from someone who was dreading starting the revision of it about 3 days ago.

I messed up the quick sort question.. missed out a number (162).. and re-did it all... completed the paper.. and had about 20-15 mins to spare - w00t

If someone has trouble remembering the questions.. heres what i remember:

1)b) Use Alternating Paths to find complete matching

2)a) Why 2 dummies?
2)b) Draw the activity network with the 2 dummies.

3)a) Use Prim's and Kruskals Algorithms to find minimum spanning trees in the networks.. ensuring you highlight the order in which you added the paths.

4)a) Sort into DESC using Quick Sort
4)b) Use bin packing algorith to cut out of 1m pieces of wood

5)a) Dijkstra's Algorithm to find best path from A to H
5)b) Use Route Inspection to find the best path from A.. to A?

6)a) Find the the max flow through three different paths
6)b) Present these flows on a diagram
6)c) Use flow-augumenting algorithm to get best flow
6)d) Show this is the best flow.. (max flow-min cut)

7)a) Write the constraints... and objective function
7)b) Show the table given was the first iteration of the Simplex method
7)c) Find the second iteration
7)d) Write down the values of all variables in the second iteration...
7)e) Is this (second iteration) the optimal solution ?

End of Paper

Think all of that is right.. but dont quote me on it.

MdSalih
6. Only bits i was iffy on was: That algorithm you had to mention in the last part of the kruskals/prims question (2 i think?) - I said use dijkstra to find shortest path from either of the verticies of the laid paths to the shortest path found using prims/kruskals.

And also the Route Inspection one (Q 5) I went for Eularian. .start at A end at A as A was already even (they didn't specify :'( - i think ) - is that right? Now that i think about it.. think it was A -H.. you need to make A and H odd
That's correct. The route inspection involves starting and finishing at the same vertex. It's not the route inspection problem if you start and finish at different vertices. Also, A was already even so theres no point making it odd or you're going to have to repeat things. Altogether you had to repeat 2 arcs.
7. Yes... they said they had already laid two paths... and you had to mention an algorithm to incorporate them into your path as economically as possible.

MdSalih
8. (Original post by MdSalih)
Yes... they said they had already laid two paths... and you had to mention an algorithm to incorporate them into your path as economically as possible.

MdSalih
I said to remove AB and FI vertices and replace them with two vertices, (ab) and (fi), connect the edges to (ab) or (fi), if 2 edges (ab) or (fi) to the same vertex then choose the one of minimum weight. Find a minimum spanning tree using Kruskals then change (ab) (fi) back into A, B, F and I.
9. did anyone get 389 for the shortest route on the dijkstra algorithm? and 1421 for the route inspection?
10. What an evil paper

Im not even sure if I got a C!

Bring on the summer resits
11. Yes, those figures sound correct

MdSalih
12. I think i got 42 for the flow question, i used back flows though, dont know if ur right.

I was well scared when i didnt get an optimal solution, kinda expected it to be.

I get the same as u guys in the answers but my flow is different to everyones
13. (Original post by Adil Bhai)
I think i got 42 for the flow question, i used back flows though, dont know if ur right.
I was well scared when i didnt get an optimal solution, kinda expected it to be.
I get the same as u guys in the answers but my flow is different to everyones
I know i found a minimum cut of 40 and marked it on my diagram and tried to find a path from S to T but the cut was okay. Perhaps your paper had a typo error for one of the capacities or something as i'm not sure how you got 42.
Anyone got the question paper?
Did u get a min cut of 42?
14. (Original post by Gaz031)
I know i found a minimum cut of 40 and marked it on my diagram and tried to find a path from S to T but the cut was okay. Perhaps your paper had a typo error for one of the capacities or something as i'm not sure how you got 42.
Anyone got the question paper?
Did u get a min cut of 42?
Apparently they aren't allowed to give test papers to to students after exams (quoted from invilgilators at my college). Which I find a little weird.. only harm I see is passing on info to people who haven't sat the exam.. but surely we can recall the info from memory. Other than that its the whole tightass thing edexcel have have with their past papers... but technically we have payed for it, or have we just payed for the examination.. and the marking not the material hmmm anyway.

I remember getting 40 as max flow.. i cut through a couple places.. got 40 as min

MdSalih
15. Yeah i got the question paper with me, ill describe the flow

s to a 25
s to c 20
s to b 9
b to c 12
a to c 14
a to d 8
c to d 2
b to f 10
c to f 7
c to e 15
e to f 3
d to e 3
e to t 11
d to t 15
f to t 21

there u go!

yeah i did get min cut 42
16. (Original post by Adil Bhai)
Yeah i got the question paper with me, ill describe the flow

s to a 25
s to c 20
s to b 9
b to c 12
a to c 14
a to d 8
c to d 2
b to f 10
c to f 7
c to e 15
e to f 3
d to e 3
e to t 11
d to t 15
f to t 21

there u go!

yeah i did get min cut 42
Can you scan the question page so i can figure out where i went wrong? Thanks.

Are these the capacities or the flow?

Edit: If i'm still getting a max flow of 40, with flow augs of (SADT8),(SACDT2),(SACET11),(SACE FT1),(SCEFT2),(SBFT9),(SCFT7).
What further flow aug can u add to this?
17. you cant use a back flow if it makes the flow negative, you can only take from a edge that already has a flow going the right way. otherwise you would be going against the direction of the edge.

for the example I said a network of pipes, each pipe has a water filter that only works in one direction. sneaky huh?
18. (Original post by mik1w)
you cant use a back flow if it makes the flow negative, you can only take from a edge that already has a flow going the right way. otherwise you would be going against the direction of the edge.

for the example I said a network of pipes, each pipe has a water filter that only works in one direction. sneaky huh?
I said the flow of traffic along a system of one way streets (But in case they didnt like that one i added in brackets, alternatively the flow of water through pipes).

I feel like i'm in limbo. I don't have my final exam (M2) until Friday and i can hardly justify starting D2/P5/P6 until after that. I guess i'll just do the review exercises again and revise Bio4 for June. Wish i could take M2 tomorrow and get it over with.
I may as well go watch a DVD or something.
19. Discussion looks interesting..

Can anyone get me a look at the paper?

Aitch

[D1 guru[?] - 100 UMS in June 04!]
20. (Original post by Adil Bhai)
Yeah i got the question paper with me, ill describe the flow
Can you Scan/Write in the question

Thanks.

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Updated: January 19, 2005
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