Hey there! Sign in to join this conversationNew here? Join for free
    Offline

    0
    ReputationRep:
    (Original post by knowledgecorruptz)
    Holy ****, has anyone tried the D2 Practice Paper B?

    I mean, what on earth!? The LP question is unbalanced. so you have to turn everything into inequalities?

    And then the dynamic programming question is impossible? Honestly, did anyone here get that one correct?
    I did it a couple of weeks ago and it seemed fine, messed up on simplex but that was because of me not double checking the calculation what was wrong with the dynamic programming question?

    Mark scheme for question 5 seems wrong though now that i look back at it :confused:
    Offline

    0
    ReputationRep:
    (Original post by Lilmzbest)
    I did it a couple of weeks ago and it seemed fine, messed up on simplex but that was because of me not double checking the calculation what was wrong with the dynamic programming question?

    Mark scheme for question 5 seems wrong though now that i look back at it :confused:
    I agree on question 5, there's definitely so dominance going on here


    Posted from TSR Mobile
    Offline

    2
    ReputationRep:
    (Original post by Lilmzbest)
    I did it a couple of weeks ago and it seemed fine, messed up on simplex but that was because of me not double checking the calculation what was wrong with the dynamic programming question?

    Mark scheme for question 5 seems wrong though now that i look back at it :confused:
    Seriously? The dynamic programming went right over my head. I think I've got it now but I really hope we can just take it from a graph. Or they start us off.

    Admittedly the rest of it was just silly mistakes but the simplex went on for AGES. Usually it's one iteration. And yeah, the mark scheme seems to be answering a different question entirely for 5.
    Offline

    16
    ReputationRep:
    (Original post by Lilmzbest)
    I did it a couple of weeks ago and it seemed fine, messed up on simplex but that was because of me not double checking the calculation what was wrong with the dynamic programming question?

    Mark scheme for question 5 seems wrong though now that i look back at it :confused:
    Yeah, for question 5 are they answering a completely different question?

    Edit: Don't worry, just looked at post above and someone else said the same thing .
    Offline

    12
    ReputationRep:
    Why does converting a network into a complete network of least distances mean that the classical and practical problems are the same?
    Offline

    0
    ReputationRep:
    (Original post by Mallika)
    Why does converting a network into a complete network of least distances mean that the classical and practical problems are the same?
    Classical = Visiting each vertex only once. Practical = Visiting each vertex at least once. If you have a classical problem, then you also have a practical problem.

    The reason it gets converted to a classical problem is because the algorithms used visit each vertex only once. Nearest neighbour starts at a vertex, visits every other vertex once only and returns to the start.

    However, finding a lower bound by using RMST + 2 smallest arcs doesn't give you a classical problem - that is why they say it is not a viable solution. This is also why when dealing with inequalities, it is strict with respect to the lower bound, but inclusive of the upper bound.

    Hope this helps
    Offline

    0
    ReputationRep:
    (Original post by mathswiz:))
    I agree on question 5, there's definitely so dominance going on here


    Posted from TSR Mobile

    (Original post by knowledgecorruptz)
    Seriously? The dynamic programming went right over my head. I think I've got it now but I really hope we can just take it from a graph. Or they start us off.

    Admittedly the rest of it was just silly mistakes but the simplex went on for AGES. Usually it's one iteration. And yeah, the mark scheme seems to be answering a different question entirely for 5.

    (Original post by brittanna)
    Yeah, for question 5 are they answering a completely different question?

    Edit: Don't worry, just looked at post above and someone else said the same thing .
    Can i ask what everyone got for that? I got p = 4/11 and value = -2/11 ... dunno if it's right though
    Offline

    2
    ReputationRep:
    (Original post by smith50)
    I was stuck on the same question check post 129 on the previous page someone kindly drew a diagram
    Smith
    i still don't get it, if you have the time can you put a explanation to what he has done, thanks
    Offline

    2
    ReputationRep:
    (Original post by Lilmzbest)
    Can i ask what everyone got for that? I got p = 4/11 and value = -2/11 ... dunno if it's right though
    Yep, same here.
    Offline

    16
    ReputationRep:
    (Original post by Lilmzbest)
    Can i ask what everyone got for that? I got p = 4/11 and value = -2/11 ... dunno if it's right though
    Yeah, I got the same as well. It wasn't really a very good paper though as there weren't any proper Hungarian or transportation problem questions.
    Offline

    0
    ReputationRep:
    (Original post by knowledgecorruptz)
    Yep, same here.

    (Original post by brittanna)
    Yeah, I got the same as well. It wasn't really a very good paper though as there weren't any proper Hungarian or transportation problem questions.
    Awesome, lol i've just started ignoring mark schemes lately, they all seem to have mistakes

    Yeah the practice papers seem to focus on too much formulating linear programming and not enough actual questions
    Offline

    1
    ReputationRep:
    Could someone give me examples of a travelling salesman problem and network flows please
    Thanks,
    Smith
    Offline

    16
    ReputationRep:
    (Original post by Lilmzbest)
    Awesome, lol i've just started ignoring mark schemes lately, they all seem to have mistakes

    Yeah the practice papers seem to focus on too much formulating linear programming and not enough actual questions
    For dynamic programming, can they ever ask us minimax/ maximin questions from a table, or will they only do that with a network. I really hope we get a network rather than a table in our exam though!
    Offline

    16
    ReputationRep:
    (Original post by smith50)
    Could someone give me examples of a travelling salesman problem and network flows please
    Thanks,
    Smith
    Do you mean real life examples, or practice questions?
    Offline

    1
    ReputationRep:
    (Original post by brittanna)
    Do you mean real life examples, or practice questions?
    real life problems
    Smith
    Offline

    16
    ReputationRep:
    (Original post by smith50)
    real life problems
    Smith
    For network flows, I usually say you can model cars moving through a one way traffic system. Or water flowing though a network of pipes.

    For travelling salesman, I guess something like if an inspector wants to travel fro his office to several different restaurants in the shortest time possible and return to wherever his office is based.
    Offline

    0
    ReputationRep:
    (Original post by brittanna)
    For dynamic programming, can they ever ask us minimax/ maximin questions from a table, or will they only do that with a network. I really hope we get a network rather than a table in our exam though!
    They can ask minimax/maximin from a table? i thought it was always from a network
    Offline

    16
    ReputationRep:
    (Original post by Lilmzbest)
    They can ask minimax/maximin from a table? i thought it was always from a network
    I'm not sure. But in the textbook on the last point of the summary box, it says:

    You can use dynamic programming to solve minimax and maximin problems presented in network and table form .
    Offline

    0
    ReputationRep:
    (Original post by brittanna)
    I'm not sure. But in the textbook on the last point of the summary box, it says:

    You can use dynamic programming to solve minimax and maximin problems presented in network and table form .

    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?
    Offline

    16
    ReputationRep:
    (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?
    I don't think I've seen one either, but i'm just hoping it doesn't come up.
 
 
 
  • See more of what you like on The Student Room

    You can personalise what you see on TSR. Tell us a little about yourself to get started.

  • Poll
    Would you like to hibernate through the winter months?
  • See more of what you like on The Student Room

    You can personalise what you see on TSR. Tell us a little about yourself to get started.

  • The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

    Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

    Quick reply
    Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.