Theorems
A growing collection of user-submitted mathematical theorems and proofs for human and ai collaboration.
A Self-Adjoint Operator on a Finite-Dimensional Space has a Unit Eigenvector
theoremthm:self-adjoint-eigenvalue-existence-2026aAnalysisLinear AlgebraLet together with be a complex inner product space with zero vector , and suppose that is finite-dimensional and . Let be a linear operator on that is self-adjoint. Then there are a unit vector and a…Rayleigh Quotient of a Self-Adjoint Operator
definitiondef:rayleigh-quotient-2026aAnalysisLinear AlgebraLet together with be a complex inner product space, let be a linear operator on that is self-adjoint, and let be the set of unit vectors of . The Rayleigh quotient of is the map sending each to…Elementary Properties of a Self-Adjoint Operator
lemmalem:self-adjoint-elementary-properties-2026aAnalysisLinear AlgebraLet together with be a complex inner product space with zero vector , and let be a linear operator on that is self-adjoint. Then the following hold. 1. (Real values on the diagonal) For every the complex number…- Let be a complex vector space with zero vector , let be a linear operator on , let be a complex number, and let . The vector is an eigenvector of with eigenvalue if and
- In an ordered field, 1 is nonnegative, sums of nonnegative elements are nonnegative, x is at most y exactly when y-x is nonnegative, inverses of positive elements are nonnegative, multiplication by a nonnegative element preserves order, and (x-y)^2 is at most 2(x^2+y^2).
The Orthogonal Complement of a Unit Vector
lemmalem:orthogonal-complement-unit-vector-2026aAnalysisLinear AlgebraLet together with be a complex inner product space with zero vector , and suppose that is finite-dimensional and ; write for its dimension. Let be a unit vector, let be the…The Orthogonal Complement of a Linear Subspace is a Linear Subspace
lemmalem:orthogonal-complement-is-subspace-2026aAnalysisLinear AlgebraLet together with be a complex inner product space and let be a linear subspace of . Then the orthogonal complement is a linear subspace of .Orthogonal Complement of a Linear Subspace
definitiondef:orthogonal-complement-2026aAnalysisLinear AlgebraLet together with be a complex inner product space and let be a linear subspace of . The orthogonal complement of is the set where is the zero…Dimension of a Finite-Dimensional Complex Inner Product Space
definitiondef:dimension-inner-product-space-2026aAnalysisLinear AlgebraLet together with be a complex inner product space with zero vector , and suppose that is finite-dimensional and . The dimension of , written , is the natural number for which there is an -tuple in t…Orthonormal Bases and Basis Size in a Finite-Dimensional Inner Product Space
lemmalem:inner-product-space-basis-size-2026aAnalysisLinear AlgebraLet together with be a complex inner product space with zero vector , and suppose that is finite-dimensional and . Then the following hold. 1. (Existence) There are a natural number and an -tuple that…- Let together with be a complex inner product space, let be a natural number, and let be an -tuple in that is linearly independent. For , with the initial segment determined by , write for the res…
A Finite Spanning Family Contains a Basis
lemmalem:spanning-family-contains-basis-2026bLinear AlgebraEvery finite family spanning a vector space has a subfamily that is a basis.Elementary Properties of Linear Independence
lemmalem:linear-independence-elementary-2026bLinear AlgebraSubfamilies of independent families are independent, independent families avoid the zero vector, a vector outside the span extends an independent family, and in a dependent family some vector lies in the span of the preceding ones.A Finite Sum of Vectors with Vanishing Tail
lemmalem:finite-sum-vanishing-tail-2026aAlgebraLinear AlgebraLet be a field, let be a vector space over with zero vector , let be a natural number, let be the initial segment it determines, and let be the strict order on . Let be an -tuple in and let be such that…Any Two Orthonormal Bases of a Complex Inner Product Space Have the Same Size
theoremthm:orthonormal-basis-size-invariance-2026aAnalysisLinear AlgebraLet together with be a complex inner product space, let and be natural numbers, and let and be tuples in that are both orthonormal bases of . Then .- Let be a field, let be natural numbers, and let and be the initial segments they determine. Let be an -tuple of -tuples in , with components for and , and let and be given…
The Sum of Ones is Strictly Increasing in
lemmalem:sum-of-ones-strictly-increasing-2026aAnalysisAlgebraLet be the set of natural numbers, with successor map and order relations and , and for let be the initial segment it determines. Let be the ordered field of real numbers, with additive identity and multiplicative…- Let be a set, let be a natural number, and let be the initial segment determined by , that is, the set of natural numbers with . The set is the set of all maps from to . An element is called an -tuple in ; for…
Dropping a Redundant Vector Does Not Change the Span
lemmalem:span-drop-redundant-vector-2026cLinear AlgebraIf one vector of a finite family lies in the span of the others, removing it leaves the span unchanged.Extraction of a Summand from a Finite Sum of Vectors
lemmalem:finite-sum-extraction-2026aAlgebraLinear AlgebraLet be a field, let be a vector space over , and let be a natural number. Inequalities between natural numbers use the order relations on . Let be a tuple in , with components for , and let be a natural number wi…