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# D2 Critical Path Analysis watch

1. Can anybody explain to me, where you put dummy arcs, I can never seem to get them right!

Thanks,
Klaxoii

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2. yeahhh
3. (Original post by Klaxoii)
Can anybody explain to me, where you put dummy arcs, I can never seem to get them right!

Thanks,
Klaxoii

Posted from TSR Mobile
Dummy events are used to preserve precedence. Also, the activity defined by (i, j) (where i is the start event, j is the end event) must be unique, there can be no ambiguity to this.
4. You use them when one activity is followed by another activity, but you have another activity that follows both the original activity and a different activity. So, say C follows A, but D follows both B and A.

The first diagram says that D follows A and B, which is right, but it also says that C follows both A and B, which is wrong. The second diagram shows that C follows A only, but D follows both B and C.
Also, if two arcs directly join the same nodes, a dummy activity has to be used, for reasons I don't quite understand.
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5. (Original post by Juzey)
Also, if two arcs directly join the same nodes, a dummy activity has to be used, for reasons I don't quite understand.
This is why

(Original post by lizard54142)
The activity defined by (i, j) (where i is the start event, j is the end event) must be unique, there can be no ambiguity to this.
6. (Original post by Juzey)
You use them when one activity is followed by another activity, but you have another activity that follows both the original activity and a different activity. So, say C follows A, but D follows both B and A.

The first diagram says that D follows A and B, which is right, but it also says that C follows both A and B, which is wrong. The second diagram shows that C follows A only, but D follows both B and C.
Also, if two arcs directly join the same nodes, a dummy activity has to be used, for reasons I don't quite understand.
Thanks for the feedback guys, a bit more practice and I should be okay with critical paths

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