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Vector space

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A vector space, also known as a linear space, is a fundamental mathematical structure. It consists of a set of elements called vectors. These vectors can be combined using two specific operations. The first is vector addition, which joins two vectors to create a third. The second is scalar multiplication, which scales a vector by a number called a scalar. This structure is the backbone of linear algebra. It allows mathematicians to study systems of linear equations in a concise way.

Vector add scale
Vector add scale

To qualify as a vector space, the set must satisfy eight specific requirements known as axioms. These axioms ensure the operations are consistent and predictable. The first group of axioms governs vector addition. These include associativity, commutativity, and the existence of an identity element called the zero vector. There must also be an additive inverse for every vector, which allows for subtraction. The second group of axioms governs scalar multiplication. These ensure that scaling a vector works correctly with field multiplication and addition. For example, scaling a sum of two vectors must be the same as scaling them individually.

Linear subspaces with shading
Linear subspaces with shading

Vector spaces are categorized by the type of scalars they use. If the scalars are real numbers, it is a real vector space. If the scalars are complex numbers, it is a complex vector space. More generally, a vector space can be defined over any mathematical field. These spaces can also be given extra structures. Some become algebras, such as polynomial rings or Lie algebras. Others become topological vector spaces, like Hilbert spaces or Banach spaces. These advanced versions allow for the study of functions and limits.

Every vector space has a property called dimension. This value specifies the number of independent directions within the space. A space is finite-dimensional if its dimension is a natural number. These are common in geometry and physics. For instance, arrows in a plane form a two-dimensional space.

Vector components and base change
Vector components and base change

Other spaces are infinite-dimensional. In these cases, the dimension is an infinite cardinal. Polynomial rings are an example of a countably infinite-dimensional space. Some function spaces have a dimension equal to the cardinality of the continuum.

The history of these ideas spans several centuries of mathematical discovery. In 1636, René Descartes and Pierre de Fermat founded analytic geometry. They linked equations to points on a plane. In 1844, Hermann Grassmann studied abstract objects and introduced linear independence and dimension. He even explored concepts that led to modern algebras. In 1857, Arthur Cayley introduced matrix notation. This allowed for the simplification of linear maps.

Matrix
Matrix

The first modern definition of vector spaces came from Giuseppe Peano in 1888. He originally called them "linear systems." Later, mathematicians like Henri Lebesgue, Stefan Banach, and David Hilbert formalized the study of function spaces around 1920.

To navigate a vector space, mathematicians use a tool called a basis. A basis is a subset of vectors that are linearly independent and span the entire space. This means every vector in the space can be written as a unique linear combination of the basis vectors. The scalars used in this combination are called coordinates.

Vector components
Vector components

Using a basis creates an isomorphism, which is a perfect one-to-one correspondence. This allows us to turn geometric problems into numerical ones. We can represent vectors as coordinate vectors, which are lists of numbers. This transformation makes complex computations possible.

Vector spaces connect many different fields of science and math. In physics, they are used to model quantities like force and velocity. These quantities have both a magnitude and a direction. In higher mathematics, the concept of a subspace is vital. A subspace is a smaller part of a vector space that is also a vector space. It must be closed under addition and scalar multiplication. This means any combination of vectors in the subspace stays within that same subspace.

Example for addition of functions
Example for addition of functions

This interconnectedness makes the vector space one of the most important tools in modern science.

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🖼️ Images & Media (13)
File:Vector add scale.svg
Vector add scale.svg
File:Vector components and base change.svg
Vector components and base change.svg
File:Example for addition of functions.svg
Example for addition of functions.svg
File:Vector components.svg
Vector components.svg
File:Matrix.svg
Matrix.svg
File:Determinant parallelepiped.svg
Determinant parallelepiped.svg
File:Linear subspaces with shading.svg
Linear subspaces with shading.svg
File:Universal tensor prod.svg
Universal tensor prod.svg
File:Vector norms2.svg
Vector norms2.svg
File:Periodic identity function.gif
Periodic identity function.gif
File:Rectangular hyperbola.svg
Rectangular hyperbola.svg
File:Mobius strip illus.svg
Mobius strip illus.svg

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