Lauricella's theorem

Lauricella's theorem In the theory of orthogonal functions, Lauricella's theorem provides a condition for checking the closure of a set of orthogonal functions, namely: Theorem. A necessary and sufficient condition that a normal orthogonal set {displaystyle {u_{k}}} be closed is that the formal series for each function of a known closed normal orthogonal set {displaystyle {v_{k}}} in terms of {displaystyle {u_{k}}} converge in the mean to that function.

The theorem was proved by Giuseppe Lauricella in 1912.

References G. Lauricella: Sulla chiusura dei sistemi di funzioni ortogonali, Rendiconti dei Lincei, Series 5, Vol. 21 (1912), pp. 675–85. hide vte Functional analysis (topics – glossary) Spaces BanachBesovFréchetHilbertHölderNuclearOrliczSchwartzSobolevtopological vector Properties barrelledcompletedual (algebraic/topological)locally convexreflexiveseparable Theorems Hahn–BanachRiesz representationclosed graphuniform boundedness principleKakutani fixed-pointKrein–Milmanmin–maxGelfand–NaimarkBanach–Alaoglu Operators adjointboundedcompactHilbert–Schmidtnormalnucleartrace classtransposeunboundedunitary Algebras Banach algebraC*-algebraspectrum of a C*-algebraoperator algebragroup algebra of a locally compact groupvon Neumann algebra Open problems invariant subspace problemMahler's conjecture Applications Hardy spacespectral theory of ordinary differential equationsheat kernelindex theoremcalculus of variationsfunctional calculusintegral operatorJones polynomialtopological quantum field theorynoncommutative geometryRiemann hypothesisdistribution (or generalized functions) Advanced topics approximation propertybalanced setChoquet theoryweak topologyBanach–Mazur distanceTomita–Takesaki theory Categories: Theorems in functional analysis