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Hilbert, Schmidt and the Spectral Theorem

2 minute read

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The Spectral Theorem comes in many flavors, one might encounter it first in it’s finite dimensional case, for $\mathbb{C}^n$. If $T:\mathbb{C}^n \to \mathbb{C}^n$ is a self-adjoint linear map then there is a basis ${x_1, …, x_n}$ of $\mathbb{C}^n$ consisting of eigenvectors of $T$ with which we have: \(Tx= \sum_{i=1}^n \lambda_i \langle x, x_i\rangle x_i.\) As its name suggests, it falls to Spectral Theory to extend this result into infinite dimensional spaces. As it’s usually the case, this brings forth considerable difficulties. One way of easing these difficulties is to retain some notion of finitude, in this case compactness.

The spectrum and bounded self-adjointness

1 minute read

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The spectrum $\sigma(T)$ of operators $T$ helps us them, and many of the problems spectral theorists face involve restraining this set $\sigma(T)$.

Compact operators and the unit ball

1 minute read

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One famous fact in functional analysis is that the closed unit ball $B_X$ of a normed space $X$ is compact if, and only if, the space $X$ is finite dimensional. As if paying homage to that, compact linear operators (operators that map bounded sets $A$ to relatively compact sets $T(A)$, where $\overline{T(A)}$ is compact), allude to both notions of compactness and finite-dimensionality.

Neumann Series

2 minute read

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Neumann series are series of bounded linear operators of the form

The spectrum of linear operators

1 minute read

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Essentially, spectral theory seeks to further the study of eigenvalues for the case of linear operators $T:X \to X$ on infinite dimensional spaces $X$.

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Bases de Riesz e séries de Fourier não harmônicas

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Curta apresentação no 30° SIICUSP (Simpósio Internacional de Iniciação Científica e Técnológica da USP) sobre o projeto de Iniciação Científica “Bases de Riesz e séries de Fourier não harmônicas”.

Como treinar o seu grafão

Published:

Seminário sobre o teorema de Ramsey finito e infinito para o grupo de seminários S4 do IME-USP.

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