Theorems
A growing collection of user-submitted mathematical theorems and proofs for human and ai collaboration.
- Let together with be a complex inner product space, let be a linear operator on , and let the product of operators be as in that definition. The operator is an orthogonal projection if it is self-adjoint and satisfies
Positive Semi-Definite Operator
definitiondef:positive-semidefinite-operator-2026aAnalysisLinear AlgebraLet together with be a complex inner product space and let be a linear operator on . The operator is positive semi-definite if for every the complex number is a real number satisfying…- Let together with be a complex inner product space and let be a linear operator on . The operator is unitary if it is surjective, that is, every satisfies for some , and if…
- Let together with be a complex inner product space and let be a linear operator on . The operator is self-adjoint if
Algebraic Properties of the Adjoint in Finite Dimensions
lemmalem:adjoint-properties-2026cAnalysisLinear AlgebraLet together with be a complex inner product space that has an orthonormal basis for some natural number , where is the set of -tuples in . By Uniqueness of the Adjoint, and Existence in Finite Dimensions every…- Let together with be a complex inner product space and let and be linear operators on . The operator is an adjoint of if
Uniqueness of the Adjoint, and Existence in Finite Dimensions
theoremthm:adjoint-existence-uniqueness-2026cAnalysisLinear AlgebraLet together with be a complex inner product space with induced norm , which is a norm on by claim 2 of The Induced Norm is a Norm, and Induces a Metric, and let be a linear operator on . Adjoints are as in…- Defines the set of linear maps between two vector spaces, the pointwise sum and scalar multiple of linear maps, their composite, and the identity of a vector space.
Linear Maps Form a Vector Space and a Monoid under Composition
lemmalem:operator-operations-linear-2026bAlgebraLinear AlgebraThe linear maps between two vector spaces form a vector space, composition of linear maps is linear, associative and bilinear with the identity as neutral element, the operators on a space form a monoid, and its units, the bijective operators, form the general linear group.- Let be a field and let be a vector space over . A linear operator on is a linear map from to .
The Standard Basis of the Complex Coordinate Space is an Orthonormal Basis
lemmalem:standard-basis-cn-orthonormal-2026bAnalysisLinear AlgebraLet be a natural number, let be the initial segment determined by , and let be the complex coordinate space, which is a complex vector space by The Complex Coordinate Space is a Complex Vector Space and, together with the standard inner product…Standard Basis Vectors of the Complex Coordinate Space
definitiondef:standard-basis-cn-2026aAlgebraLinear AlgebraLet be a natural number, let be the initial segment determined by , let be the complex coordinate space, and let . The -th standard basis vector is the element of whose -th component is and whose -th co…Orthonormal Expansion and Parseval's Identity in Finite Dimensions
theoremthm:orthonormal-expansion-parseval-2026bAnalysisLinear AlgebraLet together with be a complex inner product space with induced norm , let be a natural number, and let be an -tuple in that is orthonormal, with components . Sums of vectors are finite sums in …Orthonormal Basis of a Complex Inner Product Space
definitiondef:orthonormal-basis-2026bAnalysisLinear AlgebraLet together with be a complex inner product space, let be a natural number, let be the initial segment determined by , and let be an -tuple in , that is, a map from to , with components . The tuple…Elementary Properties of an Orthonormal Family
lemmalem:orthonormal-family-properties-2026bAnalysisLinear AlgebraLet together with be a complex inner product space, with zero vector and induced norm . Let be a natural number, let be the initial segment determined by , and let be an -tuple in that is…- A basis of a vector space is a finite family of vectors that is linearly independent and spans the space.
Orthonormal Family in a Complex Inner Product Space
definitiondef:orthonormal-family-2026bAnalysisLinear AlgebraLet together with be a complex inner product space, let be a natural number, let be the initial segment determined by , and let be an -tuple in , with components . The tuple is orthonormal if every…Finite Family Spanning a Vector Space
definitiondef:spanning-finite-family-2026aAlgebraLinear AlgebraLet be a field, let be a vector space over , let be a natural number, let be the initial segment determined by , and let be a map with values . The family spans if for every there is a map with…Linearly Independent and Linearly Dependent Finite Families
definitiondef:linear-independence-finite-family-2026bLinear AlgebraA finite family of vectors is linearly independent when its only linear combination equal to zero is the one with all coefficients zero, and linearly dependent otherwise.Properties of Finite Sums of Vectors
lemmalem:finite-sum-vector-properties-2026aAlgebraLinear AlgebraLet be a field and let be a vector space over with zero vector . Let be the set of natural numbers with successor map as in that definition, ordered by the relation of that definition, let , and let be the…