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Graph Theory Question


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#1 warnexus   Prime Members   -  Reputation: 1432

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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

 

influencegraph_zpsa257b4ac.png


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


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#2 Dragonsoulj   Crossbones+   -  Reputation: 2111

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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.



#3 warnexus   Prime Members   -  Reputation: 1432

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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.



#4 Dragonsoulj   Crossbones+   -  Reputation: 2111

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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. smile.png



#5 krinosx   Members   -  Reputation: 539

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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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