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Mathematical Methods for Physics and Engineering - Matematica.NET

Mathematical Methods for Physics and Engineering - Matematica.NET

Mathematical Methods for Physics and Engineering - Matematica.NET

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INTEGRAL TRANSFORMS13.10 In many applications in which the frequency spectrum of an analogue signal isrequired, the best that can be done is to sample the signal f(t) a finite number oftimes at fixed intervals, <strong>and</strong> then use a discrete Fourier trans<strong>for</strong>m F k to estimatediscrete points on the (true) frequency spectrum ˜f(ω).(a) By an argument that is essentially the converse of that given in section 13.1,show that, if N samples f n , beginning at t = 0 <strong>and</strong> spaced τ apart, are taken,then ˜f(2πk/(Nτ)) ≈ F k τ whereF k = √ 1 ∑N−1f n e −2πnki/N .2π(b) For the function f(t) defined by{1 <strong>for</strong> 0 ≤ t

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