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## Graph Theory Question

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### #1warnexus  Prime Members

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Posted 25 October 2013 - 10:08 PM

http://www.cprogramming.com/tutorial/computersciencetheory/graphtheory.html

The link aboves states the following statement.

Directed Graph: A directed graph is one in which edges connect nodes in only one direction.

But I see this influence graph in my discrete math textbook and I would disagree with the above statement.

in the right of the influence graph, you can see that both arrows are in opposite direction thus these edges connect nodes in both directions

Edited by warnexus, 25 October 2013 - 10:08 PM.

### #2Dragonsoulj  Members

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Posted 25 October 2013 - 10:54 PM

Each edge has only one direction it can go, which is the requirement. The second edge (arc) goes in the opposite direction, but each edge (arc) only goes in one direction.

### #3warnexus  Prime Members

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Posted 26 October 2013 - 10:29 AM

Each edge has only one direction it can go, which is the requirement. The second edge (arc) goes in the opposite direction, but each edge (arc) only goes in one direction.

Oh so that is what they meant. Thanks.

### #4Dragonsoulj  Members

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Posted 26 October 2013 - 03:25 PM

Each edge has only one direction it can go, which is the requirement. The second edge (arc) goes in the opposite direction, but each edge (arc) only goes in one direction.

Oh so that is what they meant. Thanks.

Yeah. I had to do a refresher. Wikipedia helps bring it back to the front of my memory.

### #5krinosx  Members

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Posted 28 October 2013 - 07:38 AM

Humm I know its already solved... but... just to add some arguments....

Think in each 'edge' as a relation... a relation is something "X related to Y"....

There is 2 ( at least ) kinds of Graphs... Directional ones and "Undirected ( no directional )"...

When the Graphs are 'No Directional' ones, the edge direction does not matter... for example, if you are trying to map the 'friendship' of peoples ( assuming that friendship are mutual... if A is friend of B, so B is friend of A )... so, if you build a graph to represent the friendship of 'N' peoples, it does not matter the edge direction.

But, if you are trying to find a route, in a MAP... you must consider the road direction... so if you have a 'one way' road to depart from point A and reach point B, this same road cant be used to depart from point B and reach point A... now you need the edge direction to represent the relation between  A and B...

Hum... well.. its just a bit of theory to this question...

( sry about my english )

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