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Mostrando las entradas de noviembre, 2017

Homework 16, Real Analysis

Due date: November 24 Problem 1 If the measurable fnf0 with f1<, then fnf. Explain the condition f1<. Problem 2 Let fL1(\R) and fδ(x)=f(δx). Then fδ=1δf. Problem 3 There exists a positive continuous fL1(\R) such that lim sup If f\in L^1(\R) is uniformly continuous, then \lim_{|x|\to\infty}f(x) = 0. Problem 4 If f\in L^1(\R) and F(x) = \int_{-\infty}^x f. Then  F is uniformly continuous.

Homework 15, Real Analysis

Due date: November 17 Problem 1 For each n\in\Z, let e_n(x) = e^{2\pi i nx}. Then \displaystyle \int_0^1 e_n(x) \overline{e_m(x)} dx = \begin{cases} 1 & n=m\\ 0 & n\not=m. \end{cases} Problem 2 For f\in C([0,1]), the sequence \widehat f(n) \to 0 as |n|\to\infty. Problem 3 Let f\in C^1([0,1]) with f(0)=f(1). \widehat{f'}(n) = 2\pi i n \widehat f(n) The Fourier series of  f converges uniformly to  f . Problem 4 Let E\subset \R and U_n the open set U_n = \{x\in\R: d(x,E)<1/n\}. If  E is compact, |E| = \lim |U_n|. However, the previous conclusion may be false if either  E is closed and unbounded, or bounded and open. Problem 5 Let  E be the subset of [0,1] of numbers which do not have the digit 4 in their decimal expansion. Find |E|.

Homework 14, Real Analysis

Due date: November 10 Problem 1 Let  Y be a vector subspace of the normed space  X . Then its closure \bar Y is also a vector subspace of  X . Problem 2 Let X=C([-1,1]) with the inner product \displaystyle (f,g) = \int_{-1}^1 f\bar g. Apply the Gram-Schmidt process to the sequence f_n(x) = x^n to obtain the orthonormal polynomials p_0, p_1, p_2, p_3, such that each p_n is of degree  n . These are the first  Legendre polynomials . Problem 3 Let  Y be a close subspace of the Hilbert space  X and T:X\to Y the orthogonal projection onto  Y , Tx = \text{Proj}_Y x. T is continuous. Problem 4 Let  Y be a closed subspace of the Hilbert space  X , and let Y^\perp = \{ x\in X: x\perp Y\}. Y^\perp is a closed subspace of  X . X\cong Y\oplus Y^\perp. Problem 5 Let X be an inner product space and \bar X its completion. \bar X is a Hilbert space. If  X is separable, so is $latex \ba...