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# OCR Decision 1 - 24 May 2012 Tweet

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1. Re: OCR Decision 1 - 24 May 2012
(Original post by FK_)
1i) Draw the diagram with 10 arcs
1ii) Complete Dijkstra's algorithm. Length = 49 Route : AEF
1ii) Time = 1200 seconds

2i) Draw a pentagon (eulerian with 5 arcs)
ii) 5 arcs, 5 vertices, semi-eulerian, one vertex with order 4 - hence join the vertices with order 1 together
iii) 5 arcs, 5 vertices, semi-eulerian (none order of 4).

3i) Connect up the subjects
3ii) The two odd nodes, D1 and M2 had to be in separate sessions. For the rest, you had to just following the arcs through.
iii) An arc is added between M1 D1 which forms a loop of 3 arcs. Explain logically why this is impossible.

4i) Simplex Question: add 'slack variables' and make equations with equals signs. The restrictions on s,t and u were that they had to be greater than or equal to 0
ii) iii)... Answer was 26.4
Slack for S was 2, hence there is 2 left other in constraint 1 (or something to that effect).

5i) Linear programming question - find equations of the lines
ii)Find optimal point
x=4/3
y=8/3
iii) Integer solution: x=2 and y=2 which gives a value of 12? for P...

5i) Can't remember. Find lower bound and upper bound etc.

6i) X=-0.2
ii) X decreases by 1 and goes back to X=0
iii) The algorithm gives the same root as in part i but with more decimal places and ridiculous fractions (what is the point in that question?)
iv) The algorithm has no counter. Hence, if the cubic has no real roots, the algorithm will go into an infinite loop

Seems right, except las question, cynics always have at least one real root
2. Re: OCR Decision 1 - 24 May 2012
For the last equation I just put with larger numbers it can be very time consuming xD Pretty certain I dropped that mark, I think the actual answer was it doesn't give a particularly accurate answer (using calculator functions to factorise the cubic gave an answer about 0.25 lower than the algorithm did) due to the margin for error in -0.05 - 0.05
3. Re: OCR Decision 1 - 24 May 2012
(Original post by Nathdragon5)
Yeah, same here, that'd be amazing to get 100 when you know you screwed up well, best of luck to you!
Yeah I wasted so much time misreading the question, good luck to you too
4. Re: OCR Decision 1 - 24 May 2012
(Original post by icy elemental)
For the last equation I just put with larger numbers it can be very time consuming xD Pretty certain I dropped that mark, I think the actual answer was it doesn't give a particularly accurate answer (using calculator functions to factorise the cubic gave an answer about 0.25 lower than the algorithm did) due to the margin for error in -0.05 - 0.05
Lol I wrote exactly the same hahaha
5. Re: OCR Decision 1 - 24 May 2012
(Original post by tooambitious)
Seems right, except las question, cynics always have at least one real root
Thanks, i realise now that I was thinking of the shape of a quartic not a cubic. Plus complex roots also come in pairs which makes sense now.
. Do you mind me asking what you put?
6. Re: OCR Decision 1 - 24 May 2012
(Original post by FK_)
1i) Draw the diagram with 10 arcs
1ii) Complete Dijkstra's algorithm. Length = 49 Route : AEF
1ii) Time = 1200 seconds

2i) Draw a pentagon (eulerian with 5 arcs)
ii) 5 arcs, 5 vertices, semi-eulerian, one vertex with order 4 - hence join the vertices with order 1 together
iii) 5 arcs, 5 vertices, semi-eulerian (none order of 4).

3i) Connect up the subjects
3ii) The two odd nodes, D1 and M2 had to be in separate sessions. For the rest, you had to just following the arcs through.
iii) An arc is added between M1 D1 which forms a loop of 3 arcs. Explain logically why this is impossible.

4i) Simplex Question: add 'slack variables' and make equations with equals signs. The restrictions on s,t and u were that they had to be greater than or equal to 0
ii) iii)... Answer was 26.4
Slack for S was 2, hence there is 2 left other in constraint 1 (or something to that effect).

5i) Linear programming question - find equations of the lines
ii)Find optimal point
x=4/3
y=8/3
iii) Integer solution: x=2 and y=2 which gives a value of 12? for P...

5i) Can't remember. Find lower bound and upper bound etc.

6i) X=-0.2
ii) X decreases by 1 and goes back to X=0
iii) The algorithm gives the same root as in part i but with more decimal places and ridiculous fractions (what is the point in that question?)
iv) Unsure
for 6i) wasnt it that w had to = between -0.05 and 0.05...... -0.2 isnt in that range.. i got that and then started another cycle by placing -0.2 as the input
7. Re: OCR Decision 1 - 24 May 2012
No, it was that W - X had to be in that range, a lot of people I know did that wrong.
8. Re: OCR Decision 1 - 24 May 2012
(Original post by mortaz786)
for 6i) wasnt it that w had to = between -0.05 and 0.05...... -0.2 isnt in that range.. i got that and then started another cycle by placing -0.2 as the input
Yea I mentioned this before on page 4 of this thread. I'm pretty sure it's 0.2 but I could be wrong ofc
9. Re: OCR Decision 1 - 24 May 2012
(Original post by icy elemental)
No, it was that W - X had to be in that range, a lot of people I know did that wrong.
Yeah, this is right, that's what I did, and the algorithm just kept going, luckily I realised before the end tho :P
10. Re: OCR Decision 1 - 24 May 2012
(Original post by icy elemental)
No, it was that W - X had to be in that range, a lot of people I know did that wrong.
ye but w was -0.2 and x was 0.... that stil = -0.2
11. Re: OCR Decision 1 - 24 May 2012
(Original post by mortaz786)
ye but w was -0.2 and x was 0.... that stil = -0.2
Yeah, so you do it again replacing X with -0.2 and that time it ends.

(Original post by Nathdragon5)
Yeah, this is right, that's what I did, and the algorithm just kept going, luckily I realised before the end tho :P
Pretty sure it didn't keep going... when you start with X = 0, it ended within two run throughs of the algorithm. With X = -1 it ended within three.
12. Re: OCR Decision 1 - 24 May 2012
(Original post by Lucozad)
Random Guess of grade Boundaries

A - 52
B - 47
C - 42
D - 37
E - 32
way optimistic
13. Re: OCR Decision 1 - 24 May 2012
(Original post by FK_)
Surely for the second iteration:

Therefore

Oh. Yet another silly error I made. Hopefully I won't loose too many marks for doing another iteration.
14. Re: OCR Decision 1 - 24 May 2012
(Original post by eliotball)
way optimistic
that can't be true at all.... see this:http://www.ocr.org.uk/news/2011/item_005.html#nogo
15. Re: OCR Decision 1 - 24 May 2012
wow, that went a lot worse than expected.
I got 600 for upper bound anyone else?
I couldn't finish the last part of first question so just put -0.217 as a guess ?

and for the very last question, I put if guesses are not far away enough from each other you will get the same result.
16. Re: OCR Decision 1 - 24 May 2012
uuurg that was awful, I didn't finish in time :/
So annoyed at myself that I missed that you had to convert it into minutes, easy mark lost
And Simplex should have been for waaay more marks... :/
Think I'll be lucky to get a D... but considering I only had about 5 lessons for it and taught myself most of it, I think I'm OK with that... :L There's always a resit in January!
17. Re: OCR Decision 1 - 24 May 2012
(Original post by h2shin)
wow, that went a lot worse than expected.
I got 600 for upper bound anyone else?
I couldn't finish the last part of first question so just put -0.217 as a guess ?

and for the very last question, I put if guesses are not far away enough from each other you will get the same result.
i got 600 tooo
18. Re: OCR Decision 1 - 24 May 2012
(Original post by Lucozad)
i got 600 tooo
yay !
I was worried cause I accidently did the prim's algorithm to start with so I panicked and rushed the nearest neighbour.
19. Re: OCR Decision 1 - 24 May 2012
did anyone get 590 for the nearest neighbour question?
20. Re: OCR Decision 1 - 24 May 2012
Wow, it was so time-consuming! ♥
The algorithm and simplex took so long...
It looks like everyone has had similar problems though, so hopefully it will be ok! Haha.
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