Discrete Fourier transform and inverse
For N complex coefficients aⱼ define yₖ=Σ_(j=0)^(N−1)aⱼωᴶᴷ, with ω=e²πⁱ⁄ᴺ.
Key knowledge
For N complex coefficients aⱼ define yₖ=Σ_(j=0)^(N−1)aⱼωᴶᴷ, with ω=e²πⁱ⁄ᴺ. The inverse is aⱼ=N⁻¹Σ_(k=0)^(N−1)yₖω⁻ᴶᴷ. This converts polynomial coefficients to values at the Nth roots of unity.
Conditions and scope
- Here the forward transform uses positive angular sign; other conventions reverse signs or normalization.
- The discrete transform acts on finite vectors and is distinct from a continuous Fourier integral.
Sources · 1
References
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Evidence and review
Lecture 5 section 5.1.1 roots-of-unity evaluation and section 5.1.2 inverse-matrix calculation.
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