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'''Primal graph''' may be used in several meanings.
{{unreferenced|date=June 2008}}
In [[graph theory]], the term '''primal graph''' may be used in several meanings.


*[[Primal graph (hypergraphs)]] of a [[hypergraph]]
A '''primal graph''' of a [[hypergraph]] is a [[Graph (mathematics)|graph]] with the same vertices of the hypergraph, and an edge between any pair of vertices contained in the same [[hyperedge]].
*A '''primal graph''' may be the [[planar graph]] from which a [[dual graph]] is formed.
*[[Primal constraint graph]]


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Alternatively, a primal graph may be the [[planar graph]] from which a [[dual graph]] is formed.

In [[constraint satisfaction]], the primal graph or '''primal constraint graph''' of a [[constraint satisfaction problem]] is the graph whose nodes are the variables of the problem and an edge joins a pair of variables if the two variables occur together in a constraint. The primal graph of a constraint satisfaction problem can also be defined as the primal graph of the hypergraph made of the variables and the constraint scopes. In the case of binary constraint network any two nodes having missing arcs between each other means these two nodes have the universal binary relation between each pair of values.

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[[Category:Constraint satisfaction]]
[[Category:Graphs]]

Revision as of 17:58, 10 October 2008

Primal graph may be used in several meanings.