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D2 6th June 2013

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Reply 20
Avatar for Lilmzbest
Lilmzbest
Original post by bonjour04
Aha hopefully. Just realised we have game theory too *face palm*


Game theory looks scary but actually isn't, it's just about learning how to set out a mixed strategy answer and then just practicing :smile:
Reply 21
Avatar for Lilmzbest
Lilmzbest
Anyone else finding the linear programming at the end of the chapters really annoying? I can never remember what to do for each one! :tongue:
Reply 22
Avatar for imasha.sj
imasha.sj
Original post by Lilmzbest
Oh you meant the one in the book! My bad :colondollar: i got SCBEDT, its a confusing one because both arcs BC and DE have backflow :tongue:


Since BC and DE have back flows is it possible for SCBEDT to be a flow augmenting route?
Original post by imasha.sj
Can someone please explain to me the answer to Edexcel D2 examination style paper Q 2e?

Is there any flow-augmenting route?

Thank you :smile:


Well, it says by inspection so consider the possible path.
First, you look at the arcs leading away from the source node of which only SC is not saturated.
Then, you look at the arcs from C; you can see that both CE and CF are saturated BUT you can use a backflow from CB.
Then, you get a flow through BE. Now, the only way you can arrive at T is to use DT so you use another back flow from E to D, followed by DT.
Thus, the answer is SCBEDT with value 3.

On the side, is it a bad thing that I'm going to do no work on D2 until after my C2/S2 exam on the 24th of May?
Reply 24
Avatar for imasha.sj
imasha.sj
Original post by Epic Flawless
Well, it says by inspection so consider the possible path.
First, you look at the arcs leading away from the source node of which only SC is not saturated.
Then, you look at the arcs from C; you can see that both CE and CF are saturated BUT you can use a backflow from CB.
Then, you get a flow through BE. Now, the only way you can arrive at T is to use DT so you use another back flow from E to D, followed by DT.
Thus, the answer is SCBEDT with value 3.

On the side, is it a bad thing that I'm going to do no work on D2 until after my C2/S2 exam on the 24th of May?


Thanks :smile: I don't think it' bad as long as you are confident about the subject.

Btw I don't get how a back flow can increase the value of the path.
Original post by imasha.sj
Thanks :smile: I don't think it' bad as long as you are confident about the subject.

Btw I don't get how a back flow can increase the value of the path.


This probably won't make any sense but I'll say it anyway on the off-chance:

Increasing backflow means there is more flow at the starting node (e.g. the node where the edge started). This means you can divert more flow to the other pipes that start at the node. This enables you to increase the total flow going through the path.
Reply 26
Avatar for imasha.sj
imasha.sj
Original post by knowledgecorruptz
This probably won't make any sense but I'll say it anyway on the off-chance:

Increasing backflow means there is more flow at the starting node (e.g. the node where the edge started). This means you can divert more flow to the other pipes that start at the node. This enables you to increase the total flow going through the path.


Can you please explain it a little bit more? :smile:
Original post by imasha.sj
Can you please explain it a little bit more? :smile:


Yeah it's kinda hard. Umm, well, here it goes:

Imagine this network here:

A-----------B
|
|
|
C

So let's say you're at C and you take a backflow route back to A. Because you're going the opposite way, rather than increasing the flow you are decreasing it.

This means that at point A, there is no more available flow (as less is now being given to C). This means there is more available for B, and so the flow can be increased through B, and the total value of the network flow may rise.
Reply 28
Avatar for imasha.sj
imasha.sj
Original post by knowledgecorruptz
Yeah it's kinda hard. Umm, well, here it goes:

Imagine this network here:

A-----------B
|
|
|
C

So let's say you're at C and you take a backflow route back to A. Because you're going the opposite way, rather than increasing the flow you are decreasing it.

This means that at point A, there is no more available flow (as less is now being given to C). This means there is more available for B, and so the flow can be increased through B, and the total value of the network flow may rise.


Got it!!! :biggrin: Thank you soooooo much!!!!! :smile:
Reply 29
Avatar for mattj94
mattj94
Original post by Lilmzbest
Anyone else finding the linear programming at the end of the chapters really annoying? I can never remember what to do for each one! :tongue:


I've written out methods for formulating linear programming problems on my website (with examples) which can be found here http://www.mattsrevision.com/decision-2/

Matt
Reply 30
Avatar for Lilmzbest
Lilmzbest
Original post by mattj94
I've written out methods for formulating linear programming problems on my website (with examples) which can be found here http://www.mattsrevision.com/decision-2/

Matt


Thanks for this, a nice concise explanation :smile:
Hey, has anybody done the mock paper? The mark scheme is really confusing me, especially Q5.
Original post by mattj94
I've written out methods for formulating linear programming problems on my website (with examples) which can be found here http://www.mattsrevision.com/decision-2/

Matt


Awesome. And that's it right? That's all I need to do to score full marks on a linear programming question?
Reply 33
Avatar for Arsey
Arsey
10
Original post by kashagupta
Actually so worried for this exam! Has anyone got any revision tips for it? Not many people seem to be sitting it for some reason?


http://www.thestudentroom.co.uk/showthread.php?t=2013301

A revision thread I started last year. Contains lots of papers etc.

Here is a sheet of definitions; however, don't forget any definition from D1 'could' be asked.

absolutely hammer the 3 different LP questions; Allocation, Transportation, Game theory. One is guaranteed to come up and it is gift marks if revised properly.
D2 Definitions to learn.docx14.5KB
Reply 34
Avatar for Arsey
Arsey
10
Another tip

On GT questions. If you have row domination, say row 3 is deleted. Don't forget in your final answer to say...

A should never play row 3.

Easy mark to drop.
Original post by Arsey
Another tip

On GT questions. If you have row domination, say row 3 is deleted. Don't forget in your final answer to say...

A should never play row 3.

Easy mark to drop.


Hi, do you know where I could find a list of D1 definitions? (just in case)

Also, there's a link above which summarises LP - is that really everything? I know it's decision maths but it seems too easy for the 7/8 marks that are typically awarded.
Reply 36
Avatar for Arsey
Arsey
10
Original post by knowledgecorruptz
Hi, do you know where I could find a list of D1 definitions? (just in case)

Also, there's a link above which summarises LP - is that really everything? I know it's decision maths but it seems too easy for the 7/8 marks that are typically awarded.


I haven't looked at the link yet but here are my D1 definitions
Definitions for the D1 Exam.docx16.4KB
Reply 37
Avatar for Arsey
Arsey
10
Original post by knowledgecorruptz
Hi, do you know where I could find a list of D1 definitions? (just in case)

Also, there's a link above which summarises LP - is that really everything? I know it's decision maths but it seems too easy for the 7/8 marks that are typically awarded.


pretty much, although I would use Sigma notation in the first one too. Also you ought to say what i and j are, workers, tasks etc.

You may need to put the Game Theory one into a simplex tableau too
Do is everyone ready for this exam ???? And how are you lot revising


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Reply 39
Avatar for Lilmzbest
Lilmzbest
Original post by Lubnahmasembe
Do is everyone ready for this exam ???? And how are you lot revising


Posted from TSR Mobile


I'm actually feeling quite good for this exam, for me i just make stupid calculation mistakes so i'm practicing doing things slowly and checking as i go along :smile: Otherwise i think the content is quite easy compared to other modules :tongue:

How's your revision going? :smile:

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