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# Edexcel D1 Jan 23 2013 Revision thread watch

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1. (Original post by Ollie.loney)
Just a quick question. In flow chart style questions when should you begin a new row in the table. ?
Would really like to know the answer to this^

When you're following an algorithm with steps, I generally start a new row for each new step, but sometimes they do it differently in the book.
2. (Original post by Ollie.loney)
Just a quick question. In flow chart style questions when should you begin a new row in the table. ?
In a Gantt Chart, you first do the critical activities in a single bar from time 0 to critical time. (If there are more critical activities which doesn't fit in a single row which means there are more than one critical paths, just put it under the first raw.)

Then alphabetically move to a new row below for each activity. All the individual bars should be under the critical activity bar.
3. (Original post by thephysicsguy)
In a Gantt Chart, you first do the critical activities in a single bar from time 0 to critical time. (If there are more critical activities which doesn't fit in a single row which means there are more than one critical paths, just put it under the first raw.)

Then alphabetically move to a new row below for each activity. All the individual bars should be under the critical activity bar.
I'm pretty sure they are talking about something like this:

P.s. I also want to know the answer to this question
4. (Original post by Kishan91)
I'm pretty sure they are talking about something like this:

P.s. I also want to know the answer to this question
Yep, can anyone clarify? Is there a formal way of doing it? I've seen it done so many different ways in the text book...
5. (Original post by Kishan91)
I'm pretty sure they are talking about something like this:

P.s. I also want to know the answer to this question
Ooh okay I see now, when you said chart i directly thought of critical path analysis sorry

This one I remember from Jan 10 paper.
In general there is not a formal way to do flow charts.
For answer, check the mark scheme, the thing with the marks scheme is that there are empty places after the first yes-no question.
TBH i didn't really get that one either...
6. (Original post by Ollie.loney)
Just a quick question. In flow chart style questions when should you begin a new row in the table. ?
Wow, I came on here to ask the exact same question...seems nobody knows....
7. When using Dijkstra's algorithm, would you replace the working values with higher numbers? I was told not to but it seems they do it in the mark scheme.
8. Quick question When drawing an activity network, is the start event number a 0 or a 1 as in the textbook they always start at event number 0, but in the January 2009 paper mark scheme they started at 1.

9. (Original post by FLLF)
When using Dijkstra's algorithm, would you replace the working values with higher numbers? I was told not to but it seems they do it in the mark scheme.
No you only write down smaller numbers. In the mark scheme they put larger numbers in brackets, which isn't compulsory in the exam.
10. (Original post by Kishan91)
No you only write down smaller numbers. In the mark scheme they put larger numbers in brackets, which isn't compulsory in the exam.
hi one question in dijkastras if we get 2 numbers which are the same in the 2 boxes do we order them with the same number
11. (Original post by otrivine)
hi one question in dijkastras if we get 2 numbers which are the same in the 2 boxes do we order them with the same number
If you have your Edexcel D1 textbook look at the diagram on page 55 - answers the question.

No you don't order them with the same number, i.e. if vertex A and B have 8 in the box, do the stuff at A and label it 2 and then do the stuff at B and label it 3
12. (Original post by Kishan91)
If you have your Edexcel D1 textbook look at the diagram on page 55 - answers the question.

No you don't order them with the same number, i.e. if vertex A and B have 8 in the box, do the stuff at A and label it 2 and then do the stuff at B and label it 3
I don't have the text book, so what's the answer? :P

My teacher told me its down to personal preference and doesn't make a difference. But if Edexcel use 1 as the start I suppose it's safe to use that.
13. (Original post by kanojyoxx)
I don't have the text book, so what's the answer? :P

My teacher told me its down to personal preference and doesn't make a difference. But if Edexcel use 1 as the start I suppose it's safe to use that.
I'll probably just start it with a 1 then. Thanks
14. I just noticed something with the January 2011 D1 paper.

For question 4: It asks to find an improved matching, so I found an improved matching from D (left side) to 1 (right side). I then found a complete matching from this.

However, in the mark-scheme the only alternative answers listed are from J to an unmatched node in the other set.
It says: 1M1: Path from J to 1 or 4 (or vice versa).

But, my final answers for the complete matching are the same as in the mark scheme .

Paper Q4: http://tinyurl.com/aseknz2
Mark scheme: http://tinyurl.com/bcysz3a
15. (Original post by Kishan91)
I just noticed something with the January 2011 D1 paper.

For question 4: It asks to find an improved matching, so I found an improved matching from D (left side) to 1 (right side). I then found a complete matching from this.

However, in the mark-scheme the only alternative answers listed are from J to an unmatched node in the other set.
It says: 1M1: Path from J to 1 or 4 (or vice versa).

But, my final answers for the complete matching are the same as in the mark scheme .

Paper Q4: http://tinyurl.com/aseknz2
Mark scheme: http://tinyurl.com/bcysz3a
I remember doing this question and I couldn't find an alternating path from D...what was yours?
16. (Original post by knowledgecorruptz)
I remember doing this question and I couldn't find an alternating path from D...what was yours?
Improved matching:

D-2 = A - 5 = M - 1 Breakthrough has occurred
Change status: D=2-A=5-M=1

A = 5
B = 3
D = 2
J = unmatched
K = 6
M = 1

Complete matching:

J -3=B-1=M-5=A-6=K-4 Breakthrough has occurred
Change status: J=3-B=1-M=5-A=6-K=4

A = 6
B = 1
D = 2
J = 3
K = 4
M = 5
17. (Original post by Kishan91)
Improved matching:

D-2 = A - 5 = M - 1 Breakthrough has occurred
Change status: D=2-A=5-M=1

A = 5
B = 3
D = 2
J = unmatched
K = 6
M = 1

Complete matching:

J -3=B-1=M-5=A-6=K-4 Breakthrough has occurred
Change status: J=3-B=1-M=5-A=6-K=4

A = 6
B = 1
D = 2
J = 3
K = 4
M = 5
How can M go to 1??

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18. (Original post by knowledgecorruptz)
How can M go to 1??

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Oh my gawd...I thought it joined to 1 instead of 2...I'm a fool

Thanks a lot for pointing that out

I hope I don't make a stupid mistake like this in the actual exam.
19. (Original post by Kishan91)
Oh my gawd...I thought it joined to 1 instead of 2...I'm a fool

Thanks a lot for pointing that out

I hope I don't make a stupid mistake like this in the actual exam.
Yeah, I'm pretty worried about that as well. I'll just have to be extra-pedantic and trace all the lines to make sure.
20. (Original post by Kishan91)
No you only write down smaller numbers. In the mark scheme they put larger numbers in brackets, which isn't compulsory in the exam.
Cheers, I was wondering if you could clear one other thing up.

When using kruskals and you have to select arcs, what happens if they're both the same weight? Do you show them both in the same bracket to show they're considered at the same time?

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