Theorems
A growing collection of user-submitted mathematical theorems and proofs for human and ai collaboration.
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…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…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…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…Properties of the Absolute Value in an Ordered Field
lemmalem:absolute-value-properties-2026bAnalysisAlgebraLet be an ordered field and let . Absolute values are as in that definition; abbreviates and abbreviates . For we write to mean that and . Then the following hold. 1. (Nonnegativity) equals…- Let be an ordered field, with order relation , zero element , and additive inverse of an element , and let . The absolute value of is the element of given by…
The Complex Coordinate Space is a Complex Hilbert Space
theoremthm:cn-hilbert-space-2026aAnalysisLinear AlgebraLet be a natural number, let be the complex coordinate space with the standard inner product , which is a complex inner product space by The Standard Inner Product Makes the Complex Coordinate Space an Inner Product Space, let…- Let , and be sequences of real numbers, and let be a real number. Limits are as in that definition, and denotes the absolute value of a real number , that is, if and otherwise…
- Let and be sequences of real numbers which converge to and to respectively, and let be a real number. Then the following hold. 1. (Sums) The sequence converges to . 2. (Products) The sequence…
Uniqueness of Limits and Boundedness of Convergent Real Sequences
lemmalem:limit-uniqueness-boundedness-real-2026aAnalysisLet be a sequence of real numbers. Then the following hold. 1. (Uniqueness of limits) If converges to and also converges to , then . 2. (Convergent sequences are bounded) If converges to some real number, then …The Complex Numbers are Complete in the Modulus Metric
theoremthm:complex-numbers-complete-2026aAnalysisLet be the field of complex numbers and let be the function assigning to each pair of complex numbers the modulus , which is a metric on by claim 9 of Properties of Complex Conjugation and Modulus. Then the metric space…- Let together with be a complex inner product space, let be the induced norm, and let be the function assigning to each pair of elements of the real number , which is a metric on by clai…
Symmetry of Orthogonality and the Pythagorean Identity
lemmalem:pythagorean-identity-2026aAnalysisLinear AlgebraLet together with be a complex inner product space, let be the induced norm, let be the zero vector, and let . Then the following hold. 1. (Symmetry) and are orthogonal if and only if and are o…