Μεταθετικόν Διάγραμμα
- Ένα Μαθηματικό Διάγραμμα
Ετυμολογία[]
Η ονομασία "μεταθετικό" σχετίζεται ετυμολογικά με την [[λέξη] "μεταθετικότητα".
Εισαγωγή[]
In mathematics, and especially in category theory, a commutative diagram is a diagram of objects (also known as vertices) and morphisms (also known as arrows or edges) such that all directed paths in the diagram with the same start and endpoints lead to the same result by composition.
Commutative diagrams play the role in category theory that equations play in algebra (see Barr-Wells, Section 1.7).
Note that a diagram may not be commutative, i.e., the composition of different paths in the diagram may not give the same result. For clarification, phrases like "this commutative diagram" or "the diagram commutes" may be used.
Examples[]
In the bottom-left diagram, which expresses the first isomorphism theorem, commutativity means that while in the bottom-right diagram, commutativity of the square means :
Αρχείο:First isomorphism theorem (plain).svg | Αρχείο:Commutative square.svg |
For the diagram below to commute, we must have the three equalities: (1) (2) and (3) . Since the first equality follows from the last two, for the diagram to commute it suffices to show (2) and (3). However, since equality (3) does not generally follow from the other two equalities, for this diagram to commute it is generally not enough to only have equalities (1) and (2).
Αρχείο:CommutativeDiagramExample.png |
Symbols[]
In algebra texts, the type of morphism can be denoted with different arrow usages: monomorphisms with a , epimorphisms with a , and isomorphisms with a . The dashed arrow typically represents the claim that the indicated morphism exists whenever the rest of the diagram holds; the arrow may optionally be labeled . If the dashed arrow is labeled or , the morphism is furthermore unique. These conventions are common enough that texts often do not explain the meanings of the different types of arrow.
Verifying commutativity[]
Commutativity makes sense for a polygon of any finite number of sides (including just 1 or 2), and a diagram is commutative if every polygonal subdiagram is commutative.
Υποσημειώσεις[]
Εσωτερική Αρθρογραφία[]
Βιβλιογραφία[]
Ιστογραφία[]
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