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OCR MEI D1 - Please Help (Activity Networks) Watch

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    Hi
    If any could assist I'd be eternally grateful. I'm struggling with drawing activity networks, mainly knowing how many dummies to add.
    I understand that the precedence need to be preserved and that dictates where to put a dummy, I'm ok with this part.
    Is it correct to say that when linking two activities if one originates from the start node it has to include a dummy. I don't think I'm explaining myself very well, so I'll add two examples.

    In the first example a dummy hasn't been added between F and D so if I assume what I said was true before it'd be wrong.

    In the second example a dummy has been added between D and G, and the only reason I can think of why this is, is because D originates from the start node.


    Could anyone explain please?
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    I don't think the images added properly.


    Example 1

    Example 2
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    (Original post by Cupcakez18)
    I don't think the images added properly.


    Example 1

    Example 2
    I am taking D1 MEI also two activities cannot start and end at the same events, so if you define an activity as (i, j) where i is the start event, and j is the end event, this must be unique and can only be referring to one possible activity.
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    Hi
    Thanks for replying.
    Sorry if I'm being dumb here, but by my reasoning D from Example 1 doesn't start from the same place G does. I do think they end in the same place though.
    I must be wrong somewhere, so please correct me.
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    (Original post by Cupcakez18)
    Hi
    Thanks for replying.
    Sorry if I'm being dumb here, but by my reasoning D from Example 1 doesn't start from the same place G does. I do think they end in the same place though.
    I must be wrong somewhere, so please correct me.
    I don't think you actually would need to include that dummy activity to be honest with you, it isn't required, it just makes the network "nicer" (rather than a curving line for activity D). The other dummy in Example 1 IS required though, because E depends on A and B, but C only depends on A.
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    Thanks again for replying.
    Getting a bit stressed about all of this. I thought there are specific marks for including the same number of dummies or certain dummies as they dictate. Also I find if I I have a different number of dummies my start and end times for some nodes are different even if the final completion time is the same. Are you saying that there activity network is just an example of one that is correct?

    Apologies if I wasn't clear. I was trying to say that for the first example I had put an extra two dummies one between F and D and another spanning between G and J, as I was following the theory that you can't link two activities by a node if one starts from the origin.
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    (Original post by Cupcakez18)
    Thanks again for replying.
    Getting a bit stressed about all of this. I thought there are specific marks for including the same number of dummies or certain dummies as they dictate. Also I find if I I have a different number of dummies my start and end times for some nodes are different even if the final completion time is the same. Are you saying that there activity network is just an example of one that is correct?

    Apologies if I wasn't clear. I was trying to say that for the first example I had put an extra two dummies one between F and D and another spanning between G and J, as I was following the theory that you can't link two activities by a node if one starts from the origin.
    Yes, I believe that the activity network would still be correct if the dummy activity after D was omitted, the network would still work. However adding in the dummy makes the network neater. I don't think you would be marked down for having TOO MANY dummies, but you would certainly lose marks for not having enough.

    Could you attach an image of the network that you drew, so I can see what you've done?
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    (Original post by lizard54142)
    Yes, I believe that the activity network would still be correct if the dummy activity after D was omitted, the network would still work. However adding in the dummy makes the network neater. I don't think you would be marked down for having TOO MANY dummies, but you would certainly lose marks for not having enough.

    Could you attach an image of the network that you drew, so I can see what you've done?
    i agree... the dummy after D is not needed.

    this is Q5 here:

    http://www.mei.org.uk/files/papers/d109jn_3gfd.pdf
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    (Original post by the bear)
    i agree... the dummy after D is not needed.

    this is Q5 here:

    http://www.mei.org.uk/files/papers/d109jn_3gfd.pdf
    Glad someone also thinks the same! OP that dummy is not needed
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    (Original post by lizard54142)
    Glad someone also thinks the same! OP that dummy is not needed
    it is fine to draw non-straight lines in these networks. occasionally you may need to make the lines cross over... it looks bad but is not wrong.
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    (Original post by lizard54142)
    Yes, I believe that the activity network would still be correct if the dummy activity after D was omitted, the network would still work. However adding in the dummy makes the network neater. I don't think you would be marked down for having TOO MANY dummies, but you would certainly lose marks for not having enough.

    Could you attach an image of the network that you drew, so I can see what you've done?

    Here are both of mine that I drew. They're a bit messy but should be readable
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    (Original post by the bear)
    it is fine to draw non-straight lines in these networks. occasionally you may need to make the lines cross over... it looks bad but is not wrong.
    Yep, it's just a matter of presentation and taste.
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    (Original post by Cupcakez18)

    Here are both of mine that I drew. They're a bit messy but should be readable
    They both look correct to me you do have extra dummies after F and G in the first one, but this is fine and you'd still get all the marks.
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    (Original post by lizard54142)
    They both look correct to me you do have extra dummies after F and G in the first one, but this is fine and you'd still get all the marks.
    Thanks. That has made me feel much better about D1. Stupid as it sounds if my network didnt match theirs in terms of dummies I've been deducting most of the marks from the question

    would you also say it didn't matter that some of the start and end times on the nodes didn't match theirs, although the completion and critical are correct?
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    (Original post by Cupcakez18)
    Thanks. That has made me feel much better about D1. Stupid as it sounds if my network didnt match theirs in terms of dummies I've been deducting most of the marks from the question

    would you also say it didn't matter that some of the start and end times on the nodes didn't match theirs, although the completion and critical are correct?
    Yes, the start and end times (early and late) must be the same, although if you have extra dummies they would be slightly different.
 
 
 
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