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March 1

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Activity network question

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Suppose that there are two activities emanating from the source node, A and B. There is one activity C, that depends on A alone; one, D, that depends on B alone; and one, E, that depends on A and B. It isn't obvious to me how to use a dummy in this case, so what do I do?--Leon (talk) 19:50, 1 March 2017 (UTC)[reply]

Can you add some context, and say what your objective is? (I'm familiar with dummy variables, but only in the context of regression.) Maybe you could give a similar example in which you can show how a dummy is used. Loraof (talk) 17:34, 2 March 2017 (UTC)[reply]
An ASCII text diagram may help:
                  E
                  ^
                  |
                  ^
                 / \
           C <- A   B -> D
StuRat (talk) 18:16, 2 March 2017 (UTC)[reply]
I think in the particular precedence chart style the OP is referring to (there are many), each task is represented by the edge of a directed graph and each node represents a possible stage of completion. Say node 0 is nothing done, 1 is A done, 2 is B done, 3 is A and B done, 4 is A and C done, 5 is B and D done, and 6 is A, B and E done, with other nodes to be filled in as more tasks are added to make a complete diagram. Then A connects 0 to 1, B connects 0 to 2, C connects 1 to 4, D connects 2 to 5, and E connect 3 to 6. So far there is nothing to show 3 is connected to 1 and 2, so you need two dummy tasks, say X to connect 1 and 3, and Y to connect 2 and 3. Not my area of of expertise (the whole field is pretty woolly if you ask me), but hopefully that helps. --RDBury (talk) 03:50, 3 March 2017 (UTC)[reply]
It is the case that two dummy activities are needed, one connecting the end of A to the start of E and one connecting the end of B to the start of E. If there is no more work in the project, activities C, D and E will come to a common end node, i.e. nodes 4, 5 and 6 posited in RDBury's post will coalesce.→31.51.161.146 (talk) 17:45, 5 March 2017 (UTC)[reply]