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EspañolTRANSITIVE RELATION
In mathematics, a binary relation ''R'' over a set ''X'' is 'transitive' if it holds for all ''a'', ''b'', and ''c'' in ''X'', that if ''a'' is related to ''b'' and ''b'' is related to ''c'', then ''a'' is related to ''c''.
To write this in predicate logic:
:
For instance, the "greater than" relation is transitive:
:If A > B, and B > C, then A > C.
For example, "is greater than," "is at least as great as," and "is equal to" (equality) are transitive relations:
: whenever A > B and B > C, then also A > C
: whenever A ≥ B and B ≥ C, then also A ≥ C
: whenever A = B and B = C, then also A = C
On the other hand, "is the mother of" is not a transitive relation, because if Alice is the mother of Brenda, and Brenda is the mother of Claire, then Alice is not always the mother of Claire. What is more, it is antitransitive: Alice can ''never'' be the mother of Claire.
Then again, in biology we often need to consider motherhood over an arbitrary number of generations: the relation "is a matrilinear ancestor of". This ''is'' a transitive relation. More precisely, it is the transitive closure of the relation "is the mother of".
More examples of transitive relations:
★ "is a subset of" (set inclusion)
★ "divides" (divisibility)
★ "implies" (implication)
The converse of a transitive relation is always transitive: e.g. knowing that "is a subset of" is transitive and "is a superset of" is its converse, we can conclude that the latter is transitive as well.
The intersection of two transitive relations is always transitive: knowing that "was born before" and "has the same first name as" are transitive, we can conclude that "was born before and also has the same first name as" is also transitive.
The union of two transitive relations is not always transitive. For instance "was born before or has the same first name as" is not generally a transitive relation.
The complement of a transitive relation is not always transitive. For instance, while "equal to" is transitive, "not equal to" is only transitive on sets with at most two elements.
For a transitive relation the following are equivalent:
★ irreflexivity
★ asymmetry
★ being a strict partial order
★ preorder - a reflexive transitive relation
★ partial order - an antisymmetric preorder
★ total preorder - a total preorder
★ equivalence relation - a symmetric preorder
★ strict weak ordering - a strict partial order in which incomparability is an equivalence relation
★ total ordering - a total, antisymmetric transitive relation
Unlike other relation properties, no general formula that counts the number of transitive relations on a finite set is known.[1] However, there is a formula for finding the number of relations which are simultaneously reflexive, symmetric, and transitive – in other words, equivalence relations – , those which are symmetric and transitive, those which are symmetric, transitive, and antisymmetric, and those which are total, transitive, and antisymmetric. Pfeiffer[2] has made some progress in this direction, expressing relations with combinations of these properties in terms of each other, but still calculating any one is difficult.
★ transitive closure
★ transitive reduction
★ intransitivity
★ reflexive relation
★ symmetric relation
★ quasitransitive relation
★ relations on sets of two elements and less
★
★ Transitivity in Action at cut-the-knot
1. Steven R. Finch, "Transitive relations, topologies and partial orders", 2003.
2. Götz Pfeiffer, "Counting Transitive Relations", ''Journal of Integer Sequences'', Vol. 7 (2004), Article 04.3.2.
★ ''Discrete and Combinatorial Mathematics'' - Fifth Edition - by Ralph P. Grimaldi ISBN 0-201-19912-2
To write this in predicate logic:
:
For instance, the "greater than" relation is transitive:
:If A > B, and B > C, then A > C.
| Contents |
| Examples |
| Closure properties |
| Properties of transitivity |
| Other properties that require transitivity |
| Counting transitive relations |
| See also |
| External links |
| References |
Examples
For example, "is greater than," "is at least as great as," and "is equal to" (equality) are transitive relations:
: whenever A > B and B > C, then also A > C
: whenever A ≥ B and B ≥ C, then also A ≥ C
: whenever A = B and B = C, then also A = C
On the other hand, "is the mother of" is not a transitive relation, because if Alice is the mother of Brenda, and Brenda is the mother of Claire, then Alice is not always the mother of Claire. What is more, it is antitransitive: Alice can ''never'' be the mother of Claire.
Then again, in biology we often need to consider motherhood over an arbitrary number of generations: the relation "is a matrilinear ancestor of". This ''is'' a transitive relation. More precisely, it is the transitive closure of the relation "is the mother of".
More examples of transitive relations:
★ "is a subset of" (set inclusion)
★ "divides" (divisibility)
★ "implies" (implication)
Closure properties
The converse of a transitive relation is always transitive: e.g. knowing that "is a subset of" is transitive and "is a superset of" is its converse, we can conclude that the latter is transitive as well.
The intersection of two transitive relations is always transitive: knowing that "was born before" and "has the same first name as" are transitive, we can conclude that "was born before and also has the same first name as" is also transitive.
The union of two transitive relations is not always transitive. For instance "was born before or has the same first name as" is not generally a transitive relation.
The complement of a transitive relation is not always transitive. For instance, while "equal to" is transitive, "not equal to" is only transitive on sets with at most two elements.
Properties of transitivity
For a transitive relation the following are equivalent:
★ irreflexivity
★ asymmetry
★ being a strict partial order
Other properties that require transitivity
★ preorder - a reflexive transitive relation
★ partial order - an antisymmetric preorder
★ total preorder - a total preorder
★ equivalence relation - a symmetric preorder
★ strict weak ordering - a strict partial order in which incomparability is an equivalence relation
★ total ordering - a total, antisymmetric transitive relation
Counting transitive relations
Unlike other relation properties, no general formula that counts the number of transitive relations on a finite set is known.[1] However, there is a formula for finding the number of relations which are simultaneously reflexive, symmetric, and transitive – in other words, equivalence relations – , those which are symmetric and transitive, those which are symmetric, transitive, and antisymmetric, and those which are total, transitive, and antisymmetric. Pfeiffer[2] has made some progress in this direction, expressing relations with combinations of these properties in terms of each other, but still calculating any one is difficult.
See also
★ transitive closure
★ transitive reduction
★ intransitivity
★ reflexive relation
★ symmetric relation
★ quasitransitive relation
★ relations on sets of two elements and less
★
External links
★ Transitivity in Action at cut-the-knot
References
1. Steven R. Finch, "Transitive relations, topologies and partial orders", 2003.
2. Götz Pfeiffer, "Counting Transitive Relations", ''Journal of Integer Sequences'', Vol. 7 (2004), Article 04.3.2.
★ ''Discrete and Combinatorial Mathematics'' - Fifth Edition - by Ralph P. Grimaldi ISBN 0-201-19912-2
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