Examples of using Functors in English and their translations into Romanian
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Composed objects and functors.
Functors and natural transformations.
A natural transformation is a relation between two functors.
Functors sometimes appear in functional programming.
That required defining functors, which required categories.
Functors are structure-preserving maps between categories.
Morphisms in this category are natural transformations between functors.
Contravariant functors are also occasionally called cofunctors.[5].
Manipulation and visualization of objects, morphisms,categories, functors, natural transformations, universal properties.
Functors between one-object categories correspond to monoid homomorphisms.
There are many constructions in mathematics that would be functors but for the fact that they"turn morphisms around" and"reverse composition".
That is, functors must preserve identity morphisms and composition of morphisms.
In 1942- 45, Samuel Eilenberg andSaunders Mac Lane introduced categories, functors, and natural transformations as part of their work in topology, especially algebraic topology.
Nowadays, functors are used throughout modern mathematics to relate various categories.
One of the most general is in category theory.[11] The algebraic objects to which representation theory applies can be viewed asparticular kinds of categories, and the representations as functors from the object category to the category of vector spaces.
Thus, functors are important in all areas within mathematics to which category theory is applied.
Samuel Eilenberg andSaunders Mac Lane introduced the concepts of categories, functors, and natural transformations in 1942- 45 in their study of algebraic topology, with the goal of understanding the processes that preserve mathematical structure.
Functors often describe"natural constructions" and natural transformations then describe"natural homomorphisms" between two such constructions.
This shows that functors can be considered as morphisms in categories of categories, for example in the category of small categories.
Functors are often defined by universal properties; examples are the tensor product, the direct sum and direct product of groups or vector spaces, construction of free groups and modules, direct and inverse limits.
Ordinary functors are also called covariant functors in order to distinguish them from contravariant ones.
So in a sense, functors between arbitrary categories are a kind of generalization of monoid homomorphisms to categories with more than one object.
Contravariant functors on Open(X) are called presheaves on X. For instance, by assigning to every open set U the associative algebra of real-valued continuous functions on U, one obtains a presheaf of algebras on X.
One can compose functors, i.e. if F is a functor from A to B and G is a functor from B to C then one can form the composite functor G∘ F from A to C. Composition of functors is associative where defined.
Functors were first considered in algebraic topology, where algebraic objects(such as the fundamental group) are associated to topological spaces, and maps between these algebraic objects are associated to continuous maps between spaces.
Equivalences of categories, Functor Categories.
Functor- Italian translation- bab. la English-Italian dictionary.
Functor of the Royal House.
Opposite functor.
For example, the Hom functor is of the type Cop× C→ Set.