Fourier coefficients and pointwise convergence
For a 2L-periodic piecewise smooth real f, aₙ=L⁻¹∫₋ᴸᴸf(t)cos(nπt/L)dt and bₙ=L⁻¹∫₋ᴸᴸf(t)sin(nπt/L)dt.
Key knowledge
For a 2L-periodic piecewise smooth real f, aₙ=L⁻¹∫₋ᴸᴸf(t)cos(nπt/L)dt and bₙ=L⁻¹∫₋ᴸᴸf(t)sin(nπt/L)dt. The series a₀/2+Σₙ≥₁[aₙcos(nπt/L)+bₙsin(nπt/L)] converges to the mean of the two one-sided limits.
Conditions and scope
- L>0; at a continuity point the limit is f(t).
- Pointwise convergence does not alone permit termwise differentiation.
Sources · 1
References
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Evidence and review
Section 4.3.1 coefficient formulas and Theorem 4.3.1.
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