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I'm confused about why Equation 4.74 can be expressed as Equation 4.76 after the summation index is expressed as in Equation 4.75. Could somebody please explain? Thanks!

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1 Answers1

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It is just saying that $\sum_r f(r) = \sum_k \sum_{i=0}^{M-1} f(i+kM)$.

(Assuming that the rearrangement is valid, of course).

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